course Mth 173 yUG ᕹӷxassignment #005
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10:17:42 `q001. The graph of a certain function is a smooth curve passing through the points (3, 5), (7, 17) and (10, 29). Between which two points do you think the graph is steeper, on the average? Why do we say 'on the average'?
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RESPONSE --> First thing to do is find the rate between each set of points. Between (3,5) and (7,17): rise = 12 and run = 4, so rate = 3. Between (7,17) and (10,29): rise = 12, run = 3, so rate = 4. In other words, it is steeper between (7,17) and (10,29). This is an average because it does not show the rate at a specific point, but only across a general area. confidence assessment: 2
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10:19:09 Slope = rise / run. Between points (7, 17) and (10, 29) we get rise / run = (29 - 17) / (10 - 7) =12 / 3 = 4. The slope between points (3, 5) and (7, 17) is 3 / 1. (17 - 5) / (7 -3) = 12 / 4 = 3. The segment with slope 4 is the steeper. The graph being a smooth curve, slopes may vary from point to point. The slope obtained over the interval is a specific type of average of the slopes of all points between the endpoints.
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RESPONSE --> I think that pretty much covered it. self critique assessment: 3
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10:28:12 2. Answer without using a calculator: As x takes the values 2.1, 2.01, 2.001 and 2.0001, what values are taken by the expression 1 / (x - 2)? 1. As the process continues, with x getting closer and closer to 2, what happens to the values of 1 / (x-2)? 2. Will the value ever exceed a billion? Will it ever exceed one trillion billions? 3. Will it ever exceed the number of particles in the known universe? 4. Is there any number it will never exceed? 5. What does the graph of y = 1 / (x-2) look like in the vicinity of x = 2?
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RESPONSE --> 1. As x gets closer to 2, the values of 1/(x-2) gets larger. 2. Yes, the value can exceed both numbers as x gets closer and closer to 2. 3. I suppose it could, but as I don't know the number of particles in the known universe... 4. Infinity? Does that count? 5. The y values are very large and so it looks like the line is going straight up, even though there is a slope. self critique assessment: 2
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10:33:01 For x = 2.1, 2.01, 2.001, 2.0001 we see that x -2 = .1, .01, .001, .0001. Thus 1/(x -2) takes respective values 10, 100, 1000, 10,000. It is important to note that x is changing by smaller and smaller increments as it approaches 2, while the value of the function is changing by greater and greater amounts. As x gets closer in closer to 2, it will reach the values 2.00001, 2.0000001, etc.. Since we can put as many zeros as we want in .000...001 the reciprocal 100...000 can be as large as we desire. Given any number, we can exceed it. Note that the function is simply not defined for x = 2. We cannot divide 1 by 0 (try counting to 1 by 0's..You never get anywhere. It can't be done. You can count to 1 by .1's--.1, .2, .3, ..., .9, 1. You get 10. You can do similar thing for .01, .001, etc., but you just can't do it for 0). As x approaches 2 the graph approaches the vertical line x = 2; the graph itself is never vertical. That is, the graph will have a vertical asymptote at the line x = 2. As x approaches 2, therefore, 1 / (x-2) will exceed all bounds. Note that if x approaches 2 through the values 1.9, 1.99, ..., the function gives us -10, -100, etc.. So we can see that on one side of x = 2 the graph will approach +infinity, on the other it will be negative and approach -infinity.
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RESPONSE --> I forgot division by zero. Silly me. self critique assessment: 2
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10:45:45 `q003. One straight line segment connects the points (3,5) and (7,9) while another connects the points (10,2) and (50,4). From each of the four points a line segment is drawn directly down to the x axis, forming two trapezoids. Which trapezoid has the greater area? Try to justify your answer with something more precise than, for example, 'from a sketch I can see that this one is much bigger so it must have the greater area'.
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RESPONSE --> I know of two mathematical ways of solving this, and I think I'll take the shorter one. The formula (Upper base + lower base) * width / 2 gives the area. In these examples, upper base and lower base are the left and right sides of the trapezoids. Area 1: (9+5) * 4 / 2 = 28. Area 2: (4+2) * 40 / 2 = 120. So the second trapezoid from (10,2) to (50,4) has a much greater area. confidence assessment: 2
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10:47:05 Your sketch should show that while the first trapezoid averages a little more than double the altitude of the second, the second is clearly much more than twice as wide and hence has the greater area. To justify this a little more precisely, the first trapezoid, which runs from x = 3 to x = 7, is 4 units wide while the second runs from x = 10 and to x = 50 and hence has a width of 40 units. The altitudes of the first trapezoid are 5 and 9,so the average altitude of the first is 7. The average altitude of the second is the average of the altitudes 2 and 4, or 3. So the first trapezoid is over twice as high, on the average, as the first. However the second is 10 times as wide, so the second trapezoid must have the greater area. This is all the reasoning we need to answer the question. We could of course multiply average altitude by width for each trapezoid, obtaining area 7 * 4 = 28 for the first and 3 * 40 = 120 for the second. However if all we need to know is which trapezoid has a greater area, we need not bother with this step.
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RESPONSE --> Hmm, never thought about using the average altitude. Interesting. self critique assessment: 2
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10:57:58 `q004. If f(x) = x^2 (meaning 'x raised to the power 2') then which is steeper, the line segment connecting the x = 2 and x = 5 points on the graph of f(x), or the line segment connecting the x = -1 and x = 7 points on the same graph? Explain the basisof your reasoning.
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RESPONSE --> It looks like we need to compare slopes, so we use the formula rise/run = rate. Slope between x=2 and x=5: rise = 21, run = 3, so rate = 21/3 = 7. Slope between x=-1 and x=7: rise = 48, run = 8, so rate = 48/8 = 6. So the line connecting x=2 and x=5 has the steeper slope. confidence assessment: 2
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10:58:10 The line segment connecting x = 2 and the x = 5 points is steeper: Since f(x) = x^2, x = 2 gives y = 4 and x = 5 gives y = 25. The slope between the points is rise / run = (25 - 4) / (5 - 2) = 21 / 3 = 7. The line segment connecting the x = -1 point (-1,1) and the x = 7 point (7,49) has a slope of (49 - 1) / (7 - -1) = 48 / 8 = 6. The slope of the first segment is greater.
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RESPONSE --> Yep. self critique assessment: 3
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11:08:27 `q005. Suppose that every week of the current millenium you go to the jewler and obtain a certain number of grams of pure gold, which you then place in an old sock and bury in your backyard. Assume that buried gold lasts a long, long time ( this is so), that the the gold remains undisturbed (maybe, maybe not so), that no other source adds gold to your backyard (probably so), and that there was no gold in your yard before.. 1. If you construct a graph of y = the number of grams of gold in your backyard vs. t = the number of weeks since Jan. 1, 2000, with the y axis pointing up and the t axis pointing to the right, will the points on your graph lie on a level straight line, a rising straight line, a falling straight line, a line which rises faster and faster, a line which rises but more and more slowly, a line which falls faster and faster, or a line which falls but more and more slowly? 2. Answer the same question assuming that every week you bury 1 more gram than you did the previous week. {}3. Answer the same question assuming that every week you bury half the amount you did the previous week.
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RESPONSE --> 1. The line should rise at a continual rate if you buy the same amount of gold each week, so a rising straight line. 2. The line would rise faster and faster as the change (or the rise) would increase each week. 3. This line would rise more and more slowly as less gold is buried each week. confidence assessment: 2
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11:08:58 1. If it's the same amount each week it would be a straight line. 2. Buying gold every week, the amount of gold will always increase. Since you buy more each week the rate of increase will keep increasing. So the graph will increase, and at an increasing rate. 3. Buying gold every week, the amount of gold won't ever decrease. Since you buy less each week the rate of increase will just keep falling. So the graph will increase, but at a decreasing rate. This graph will in fact approach a horizontal asymptote, since we have a geometric progression which implies an exponential function.
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RESPONSE --> I think I got it right. self critique assessment: 2
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11:11:26 `q006. Suppose that every week you go to the jewler and obtain a certain number of grams of pure gold, which you then place in an old sock and bury in your backyard. Assume that buried gold lasts a long, long time, that the the gold remains undisturbed, and that no other source adds gold to your backyard. 1. If you graph the rate at which gold is accumulating from week to week vs. tne number of weeks since Jan 1, 2000, will the points on your graph lie on a level straight line, a rising straight line, a falling straight line, a line which rises faster and faster, a line which rises but more and more slowly, a line which falls faster and faster, or a line which falls but more and more slowly? 2. Answer the same question assuming that every week you bury 1 more gram than you did the previous week. 3. Answer the same question assuming that every week you bury half the amount you did the previous week.
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RESPONSE --> Hmm, did I do this already? 1. The line should be a rising straight line. 2. The line should be a line which rises faster and faster. 3. The line still rises, but more and more slowly. confidence assessment: 2
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11:13:28 This set of questions is different from the preceding set. This question now asks about a graph of rate vs. time, whereas the last was about the graph of quantity vs. time. Question 1: This question concerns the graph of the rate at which gold accumulates, which in this case, since you buy the same amount eact week, is constant. The graph would be a horizontal straight line. Question 2: Each week you buy one more gram than the week before, so the rate goes up each week by 1 gram per week. You thus get a risingstraight line because the increase in the rate is the same from one week to the next. Question 3. Since half the previous amount will be half of a declining amount, the rate will decrease while remaining positive, so the graph remains positive as it decreases more and more slowly. The rate approaches but never reaches zero.
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RESPONSE --> I didn't read it carefully enough. It makes sense, I just didn't read it right. self critique assessment: 2
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11:21:14 ``q007. If the depth of water in a container is given, in centimeters, by 100 - 2 t + .01 t^2, where t is clock time in seconds, then what are the depths at clock times t = 30, t = 40 and t = 60? On the average is depth changing more rapidly during the first time interval or the second?
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RESPONSE --> During the first interval, the time change (run) is 10 and the depth change (rise) is 50, so the rate is 50/10 = 5. During the second interval, the time change is 20 and the depth change is 160, so the rate is 160/20 = 8. Therefore the depth change is greater during the second time interval. self critique assessment: 2
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11:22:32 At t = 30 we get depth = 100 - 2 t + .01 t^2 = 100 - 2 * 30 + .01 * 30^2 = 49. At t = 40 we get depth = 100 - 2 t + .01 t^2 = 100 - 2 * 40 + .01 * 40^2 = 36. At t = 60 we get depth = 100 - 2 t + .01 t^2 = 100 - 2 * 60 + .01 * 60^2 = 16. 49 cm - 36 cm = 13 cm change in 10 sec or 1.3 cm/s on the average. 36 cm - 16 cm = 20 cm change in 20 sec or 1.0 cm/s on the average.
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RESPONSE --> I used 0.1 in my equations rather than .01. Bad mistake, that. self critique assessment: 2
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13:38:58 `q008. If the rate at which water descends in a container is given, in cm/s, by 10 - .1 t, where t is clock time in seconds, then at what rate is water descending when t = 10, and at what rate is it descending when t = 20? How much would you therefore expect the water level to change during this 10-second interval?
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RESPONSE --> The rate when t=10 is: 10-.1(10) = 9. The rate when t=20 is: 10-.1(20) = 8. So the average rate is (9+8) / 2 = 8.5 over the 10 second period. The amount of water level change would then be 8.5 * 10 = 85 cm. confidence assessment: 1
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13:39:17 At t = 10 sec the rate function gives us 10 - .1 * 10 = 10 - 1 = 9, meaning a rate of 9 cm / sec. At t = 20 sec the rate function gives us 10 - .1 * 20 = 10 - 2 = 8, meaning a rate of 8 cm / sec. The rate never goes below 8 cm/s, so in 10 sec the change wouldn't be less than 80 cm. The rate never goes above 9 cm/s, so in 10 sec the change wouldn't be greater than 90 cm. Any answer that isn't between 80 cm and 90 cm doesn't fit the given conditions.. The rate change is a linear function of t. Therefore the average rate is the average of the two rates, or 9.5 cm/s. The average of the rates is 8.5 cm/sec. In 10 sec that would imply a change of 85 cm.
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RESPONSE --> Hey, I got it. self critique assessment: 3
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Ʃvc̨ assignment #001 001. Rates qa rates 06-01-2007
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13:46:07 `q001. You should copy and paste these instructions to a word processor for reference. However you can always view them, as well as everything else that has appeared in this box, by clicking the 'Display Everything' button. 1. For the next question or answer, you click on 'Next Question / Answer' button above the box at top left until a question has been posed. Once a question has been posed you are to answer before you click again on this button. 2. Before clicking for an answer, type your best answer to the current question into the box to the right, then clip on the 'Enter Answer' button. 3. After entering your answer you will click on 'Next Question / Answer' to view the answer to the question. Do not tamper with the information displayed in the left-hand box. 4. If your answer was incorrect, incomplete or would otherwise require revision, you will enter a self-critique. If you learned something from the answer, you need to restate it in your own words in order to reinforce your learning. If there is something you feel you should note for future reference, you should make a note in your own words. Go to the response box (the right-hand box) and type in a self-critique and/or notes, as appropriate. Do not copy and paste anything from the left-hand box, since that information will be saved in any case. 5. If you wish to save your response to your Notes file you may choose to click on the 'Save As Notes' button rather than the 'Enter Answer' button. Doing so will save your work for your future reference. Your work will be saved in a Notes file in the c:\vhmthphy folder. The title of the Notes file will also include the name you gave when you started the program. 6. After clicking either the 'Enter Response' or the 'Save as Notes' button, click on 'Next Question / Answer' and proceed in a similar manner. In the right-hand box briefly describe your understanding of these instructions, then click 'Enter Answer'.
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RESPONSE --> First read the question in the left box, then type my answer in the right box. Click on Enter Response to actually record the response. In the next screen, enter any self-critique required. If I want to save any information for myself for later, first enter it on the right then click on Save as Notes. Then proceed on by clicking on Next Question / Answer. confidence assessment: 2
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13:46:16 Your answer has been noted. Enter 'ok' in the Response Box and click on Enter Response, then click on Next Question/Answer for the first real question.
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RESPONSE --> Ok. confidence assessment: 3
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13:47:37 `q002. Note that there are 10 questions in this assignment. The questions are of increasing difficulty--the first questions are fairly easy but later questions are very tricky. The main purposes of these exercises are to refine your thinking about rates, and to see how you process challenging information. Continue as far as you can until you are completely lost. Students who are prepared for the highest-level math courses might not ever get lost. If you make $50 in 5 hr, then at what rate are you earning money?
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RESPONSE --> The rate is $5 an hour. Rate = rise / run. Rise = $50 and run = $10, so rate = $50 / 10 = $5. confidence assessment: 3
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13:47:48 The rate at which you are earning money is the number of dollars per hour you are earning. You are earning money at the rate of 50 dollars / (5 hours) = 10 dollars / hour. It is very likely that you immediately came up with the $10 / hour because almosteveryone is familiar with the concept of the pay rate, the number of dollars per hour. Note carefully that the pay rate is found by dividing the quantity earned by the time required to earn it. Time rates in general are found by dividing an accumulated quantity by the time required to accumulate it. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> Ok. confidence assessment: 3
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13:48:34 `q003.If you make $60,000 per year then how much do you make per month?
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RESPONSE --> Here the rise is $60,000 and the run is 12 months. The rate would then equal $60,000 / 12 = $5,000 a month. confidence assessment: 3
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13:48:56 Most people will very quickly see that we need to divide $60,000 by 12 months, giving us 60,000 dollars / (12 months) = 5000 dollars / month. Note that again we have found a time rate, dividing the accumulated quantity by the time required to accumulate it. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> Ok. Seems fine. confidence assessment: 3
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13:50:00 `q004. Suppose that the $60,000 is made in a year by a small business. Would be more appropriate to say that the business makes $5000 per month, or that the business makes an average of $5000 per month?
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RESPONSE --> It would be more appropriate to say that the business made an average of $5,000 a month, since the actual rate may have varied quite dramatically. confidence assessment: 3
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13:50:15 Small businesses do not usually make the same amount of money every month. The amount made depends on the demand for the services or commodities provided by the business, and there are often seasonal fluctuations in addition to other market fluctuations. It is almost certain that a small business making $60,000 per year will make more than $5000 in some months and less than $5000 in others. Therefore it is much more appropriate to say that the business makes and average of $5000 per month. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> Ok. confidence assessment: 3
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13:52:21 `q005. If you travel 300 miles in 6 hours, at what average rate are you covering distance, and why do we say average rate instead of just plain rate?
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RESPONSE --> The rise in this equation is 300 and the run is 6 hours. The rate then equals 300 / 6 = 50 miles / hour. This is an average rate because 200 miles may have been covered in one hour and the last 100 miles may have taken 5 hours; we don't know. confidence assessment: 3
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13:52:35 The average rate is 50 miles per hour, or 50 miles / hour. This is obtained by dividing the accumulated quantity, the 300 miles, by the time required to accumulate it, obtaining ave rate = 300 miles / ( 6 hours) = 50 miles / hour. Note that the rate at which distance is covered is called speed. The car has an average speed of 50 miles/hour. We say 'average rate' in this case because it is almost certain that slight changes in pressure on the accelerator, traffic conditions and other factors ensure that the speed will sometimes be greater than 50 miles/hour and sometimes less than 50 miles/hour; the 50 miles/hour we obtain from the given information is clearly and overall average of the velocities. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> Ok. confidence assessment: 3
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13:55:06 `q006. If you use 60 gallons of gasoline on a 1200 mile trip, then at what average rate are you using gasoline, with respect to miles traveled?
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RESPONSE --> To find the rate of miles traveled per gallon of gasoline, let the rise be the 1200 miles and the run be the 60 gallons of gas. Then divide 1200 by 60 to find the miles per gallon. 1200/60 = 20 miles per gallon. confidence assessment: 2
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13:57:04 06-01-2007 13:57:04 The rate of change of one quantity with respect to another is the change in the first quantity, divided by the change in the second. As in previous examples, we found the rate at which money was made with respect to time by dividing the amount of money made by the time required to make it. By analogy, the rate at which we use fuel with respect to miles traveled is the change in the amount of fuel divided by the number of miles traveled. In this case we use 60 gallons of fuel in 1200 miles, so the average rate it 60 gal / (1200 miles) = .05 gallons / mile. Note that this question didn't ask for miles per gallon. Miles per gallon is an appropriate and common calculation, but it measures the rate at which miles are covered with respect to the amount of fuel used. Be sure you see the difference. Note that in this problem we again have here an example of a rate, but unlike previous instances this rate is not calculated with respect to time. This rate is calculated with respect to the amount of fuel used. We divide the accumulated quantity, in this case miles, by the amount of fuel required to cover those miles. Note that again we call the result of this problem an average rate because there are always at least subtle differences in driving conditions that require the use of more fuel on some miles than on others. It's very important to understand the phrase 'with respect to'. Whether the calculation makes sense or not, it is defined by the order of the terms. In this case gallons / mile tells you how many gallons you are burning, on the average, per mile. This concept is not as familiar as miles / gallon, but except for familiarity it's technically no more difficult. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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NOTES -------> Ah, I chose miles per gallon, not gallons per mile. In that case the equation was exactly reversed. ""Gallons with respect to miles"" meant gallons divided by miles, not miles divided by gallons.
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14:00:06 `q007. The word 'average' generally connotes something like adding two quantities and dividing by 2, or adding several quantities and dividing by the number of quantities we added. Why is it that we are calculating average rates but we aren't adding anything?
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RESPONSE --> We are not adding anything because the addition part has already been done since we have only been dealing with the total amount of whatever. confidence assessment: 2
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14:01:01 The word 'average' in the context of the dollars / month, miles / gallon types of questions we have been answering was used because we expect that in different months different amounts were earned, or that over different parts of the trip the gas mileage might have varied, but that if we knew all the individual quantities (e.g., the dollars earned each month, the number of gallons used with each mile) and averaged them in the usual manner, we would get the .05 gallons / mile, or the $5000 / month. In a sense we have already added up all the dollars earned in each month, or the miles traveled on each gallon, and we have obtained the total $60,000 or 1200 miles. Thus when we divide by the number of months or the number of gallons, we are in fact calculating an average rate. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> Seems pretty close. confidence assessment: 2
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14:12:45 `q008. In a study of how lifting strength is influenced by various ways of training, a study group was divided into 2 subgroups of equally matched individuals. The first group did 10 pushups per day for a year and the second group did 50 pushups per day for year. At the end of the year to lifting strength of the first group averaged 147 pounds, while that of the second group averaged 162 pounds. At what average rate did lifting strength increase per daily pushup?
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RESPONSE --> The average rate for lifting strength change per daily pushup change would set lifting strength change equal to rise and daily pushup change equal to run. In other words, the rate of lifting strength change would be: (162-147) / (50-10) = 15/40 = .375 pounds per daily pushup. confidence assessment: 1
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14:13:02 The second group had 15 pounds more lifting strength as a result of doing 40 more daily pushups than the first. The desired rate is therefore 15 pounds / 40 pushups = .375 pounds / pushup. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> confidence assessment: 3
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14:17:05 `q009. In another part of the study, participants all did 30 pushups per day, but one group did pushups with a 10-pound weight on their shoulders while the other used a 30-pound weight. At the end of the study, the first group had an average lifting strength of 171 pounds, while the second had an average lifting strength of 188 pounds. At what average rate did lifting strength increase with respect to the added shoulder weight?
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RESPONSE --> This problem is like the previous one, but ignores any change in the number of pushups. In this problem, the rise is equal to the change in lifting strength while the run is equal to the change in weight. Rise = 188 - 171 = 17. Run = 30 - 10 = 20. Rate = 17/20 = .85 pounds lifting strength per pound of weight. confidence assessment: 2
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14:17:10 The difference in lifting strength was 17 pounds, as a result of a 20 pound difference in added weight. The average rate at which strength increases with respect added weight would therefore be 17 lifting pounds / (20 added pounds) = .85 lifting pounds / added pound. The strength advantage was .85 lifting pounds per pound of added weight, on the average. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> confidence assessment: 3
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14:23:43 `q010. During a race, a runner passes the 100-meter mark 12 seconds after the start and the 200-meter mark 22 seconds after the start. At what average rate was the runner covering distance between those two positions?
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RESPONSE --> The rise should be the change in distance between the two points, which in this case is 200-100= 100m. The run should be the change in time, which is 22-12 = 10 seconds. The average rate is then the distance divided by the time: 100 / 10 = 10 m/s. confidence assessment: 2
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14:23:51 The runner traveled 100 meters between the two positions, and required 10 seconds to do so. The average rate at which the runner was covering distance was therefore 100 meters / (10 seconds) = 10 meters / second. Again this is an average rate; at different positions in his stride the runner would clearly be traveling at slightly different speeds. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> confidence assessment: 3
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14:26:14 `q011. During a race, a runner passes the 100-meter mark moving at 10 meters / second, and the 200-meter mark moving at 9 meters / second. What is your best estimate of how long it takes the runner to cover the 100 meter distance?
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RESPONSE --> First we have to find the average speed between the two points. The initial speed is 10m/s and the final speed is 9m/s, so add and divide by two: (10+9) / 2 = 9.5m/s average speed. We know the distance is 100m, so dividing the distance by the rate should give us the time it took him to run the distance: 100/9.5 = 10.53 seconds (rounded). confidence assessment: 2
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14:26:31 At 10 meters/sec, the runner would require 10 seconds to travel 100 meters. However the runner seems to be slowing, and will therefore require more than 10 seconds to travel the 100 meters. We don't know what the runner's average speed is, we only know that it goes from 10 m/s to 9 m/s. The simplest estimate we could make would be that the average speed is the average of 10 m/s and 9 m/s, or (10 m/s + 9 m/s ) / 2 = 9.5 m/s. Taking this approximation as the average rate, the time required to travel 100 meters will be (100 meters) / (9.5 m/s) = 10.5 sec, approx.. Note that simply averaging the 10 m/s and the 9 m/s might not be the best way to approximate the average rate--for example we if we knew enough about the situation we might expect that this runner would maintain the 10 m/s for most of the remaining 100 meters, and simply tire during the last few seconds. However we were not given this information, and we don't add extraneous assumptions without good cause. So the approximation we used here is pretty close to the best we can do with the given information. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> confidence assessment: 3
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14:28:44 `q012. We just averaged two quantities, adding them in dividing by 2, to find an average rate. We didn't do that before. Why we do it now?
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RESPONSE --> Because we were given two points and we needed to find the change between those two points. confidence assessment: 1
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14:28:56 In previous examples the quantities weren't rates. We were given the amount of change of some accumulating quantity, and the change in time or in some other quantity on which the first was dependent (e.g., dollars and months, miles and gallons). Here we are given 2 rates, 10 m/s and 9 m/s, in a situation where we need an average rate in order to answer a question. Within this context, averaging the 2 rates was an appropriate tactic. You need to make note of anything in the given solution that you didn't understand when you solved the problem. If new ideas have been introduced in the solution, you need to note them. If you notice an error in your own thinking then you need to note that. In your own words, explain anything you didn't already understand and save your response as Notes.
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RESPONSE --> confidence assessment: 3
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ЬJʴܲۮōqޟɴ assignment #001 001. Areas qa areas volumes misc 06-01-2007
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14:30:57 `q001. There are 11 questions and 7 summary questions in this assignment. What is the area of a rectangle whose dimensions are 4 m by 3 meters.
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RESPONSE --> The area is 4*3=12m^2. confidence assessment: 3
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14:31:13 A 4 m by 3 m rectangle can be divided into 3 rows of 4 squares, each 1 meter on a side. This makes 3 * 4 = 12 such squares. Each 1 meter square has an area of 1 square meter, or 1 m^2. The total area of the rectangle is therefore 12 square meters, or 12 m^2. The formula for the area of a rectangle is A = L * W, where L is the length and W the width of the rectangle. Applying this formula to the present problem we obtain area A = L * W = 4 m * 3 m = (4 * 3) ( m * m ) = 12 m^2. Note the use of the unit m, standing for meters, in the entire calculation. Note that m * m = m^2.
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RESPONSE --> self critique assessment: 3
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14:32:00 `q002. What is the area of a right triangle whose legs are 4.0 meters and 3.0 meters?
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RESPONSE --> Formula for area of a right triangle: (L*W)/2. (4*3)/2 = 6m^2. confidence assessment: 2
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14:32:22 A right triangle can be joined along its hypotenuse with another identical right triangle to form a rectangle. In this case the rectangle would have dimensions 4.0 meters by 3.0 meters, and would be divided by any diagonal into two identical right triangles with legs of 4.0 meters and 3.0 meters. The rectangle will have area A = L * W = 4.0 m * 3.0 m = 12 m^2, as explained in the preceding problem. Each of the two right triangles, since they are identical, will therefore have half this area, or 1/2 * 12 m^2 = 6.0 m^2. The formula for the area of a right triangle with base b and altitude h is A = 1/2 * b * h.
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RESPONSE --> Ok. self critique assessment: 3
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14:39:50 `q003. What is the area of a parallelogram whose base is 5.0 meters and whose altitude is 2.0 meters?
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RESPONSE --> Area = B*H for a parallelogram, so 5*2 = 10m^2. confidence assessment: 2
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14:39:57 A parallelogram is easily rearranged into a rectangle by 'cutting off' the protruding end, turning that portion upside down and joining it to the other end. Hopefully you are familiar with this construction. In any case the resulting rectangle has sides equal to the base and the altitude so its area is A = b * h. The present rectangle has area A = 5.0 m * 2.0 m = 10 m^2.
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RESPONSE --> Ok. self critique assessment: 3
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14:41:08 `q004. What is the area of a triangle whose base is 5.0 cm and whose altitude is 2.0 cm?
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RESPONSE --> To find the area of a triangle use Area = 1/2(bh). Area = 1/2(5*2) = 5cm^2. confidence assessment: 3
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14:42:58 It is possible to join any triangle with an identical copy of itself to construct a parallelogram whose base and altitude are equal to the base and altitude of the triangle. The area of the parallelogram is A = b * h, so the area of each of the two identical triangles formed by 'cutting' the parallelogram about the approriate diagonal is A = 1/2 * b * h. The area of the present triangle is therefore A = 1/2 * 5.0 cm * 2.0 cm = 1/2 * 10 cm^2 = 5.0 cm^2.
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RESPONSE --> Ok. self critique assessment: 3
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14:45:49 `q005. What is the area of a trapezoid with a width of 4.0 km and average altitude of 5.0 km?
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RESPONSE --> Area = Avg altitude * width, since the odd ends of the trapeziod can be cut off to form another small square. Area = 4 * 5 = 20km^2. confidence assessment: 3
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14:45:57 Any trapezoid can be reconstructed to form a rectangle whose width is equal to that of the trapezoid and whose altitude is equal to the average of the two altitudes of the trapezoid. The area of the rectangle, and therefore the trapezoid, is therefore A = base * average altitude. In the present case this area is A = 4.0 km * 5.0 km = 20 km^2.
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RESPONSE --> Ok. self critique assessment: 3
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14:49:32 `q006. What is the area of a trapezoid whose width is 4 cm in whose altitudes are 3.0 cm and 8.0 cm?
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RESPONSE --> To find the area of a trapeziod, we need the width and then the average altitude. To find the average altitude, add the two altitudes and divide by 2: (3+8)/2 = 5.5cm. Then Area = 4*5.5 = 22cm^2. confidence assessment: 2
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14:49:39 The area is equal to the product of the width and the average altitude. Average altitude is (3 cm + 8 cm) / 2 = 5.5 cm so the area of the trapezoid is A = 4 cm * 5.5 cm = 22 cm^2.
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RESPONSE --> Ok. self critique assessment: 3
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14:52:44 `q007. What is the area of a circle whose radius is 3.00 cm?
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RESPONSE --> The area of a circle is found with the equation A = (pi)r^2. Simply plug and chug. Area = (pi)(3)^2 = 28.27cm^2. confidence assessment: 3
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14:53:25 The area of a circle is A = pi * r^2, where r is the radius. Thus A = pi * (3 cm)^2 = 9 pi cm^2. Note that the units are cm^2, since the cm unit is part r, which is squared. The expression 9 pi cm^2 is exact. Any decimal equivalent is an approximation. Using the 3-significant-figure approximation pi = 3.14 we find that the approximate area is A = 9 pi cm^2 = 9 * 3.14 cm^2 = 28.26 cm^2, which we round to 28.3 cm^2 to match the number of significant figures in the given radius. Be careful not to confuse the formula A = pi r^2, which gives area in square units, with the formula C = 2 pi r for the circumference. The latter gives a result which is in units of radius, rather than square units. Area is measured in square units; if you get an answer which is not in square units this tips you off to the fact that you've made an error somewhere.
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RESPONSE --> I rounded, which I should not have done. self critique assessment: 2
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14:54:40 `q008. What is the circumference of a circle whose radius is exactly 3 cm?
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RESPONSE --> Thanks to your prior answer C = 2*pi*r. C = 2*pi*3 = 6pi cm or rounded to 18.8cm. confidence assessment: 2
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14:54:52 The circumference of this circle is C = 2 pi r = 2 pi * 3 cm = 6 pi cm. This is the exact area. An approximation to 3 significant figures is 6 * 3.14 cm = 18.84 cm. Note that circumference is measured in the same units as radius, in this case cm, and not in cm^2. If your calculation gives you cm^2 then you know you've done something wrong.
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RESPONSE --> Yep. self critique assessment: 3
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14:56:51 `q009. What is the area of a circle whose diameter is exactly 12 meters?
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RESPONSE --> Diameter is equal to 2r, and we need r to find the area of a circle. Therefore, r = 12m/2 = 6m. Area = pi*r^2 = pi*6^2 = 36pi cm^2. confidence assessment: 3
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14:57:29 The area of a circle is A = pi r^2, where r is the radius. The radius of this circle is half the 12 m diameter, or 6 m. So the area is A = pi ( 6 m )^2 = 36 pi m^2. This result can be approximated to any desired accuracy by using a sufficient number of significant figures in our approximation of pi. For example using the 5-significant-figure approximation pi = 3.1416 we obtain A = 36 m^2 * 3.1416 = 113.09 m^2.
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RESPONSE --> I put in cm^2 instead of m^2. self critique assessment: 2
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15:04:12 `q010. What is the area of a circle whose circumference is 14 `pi meters?
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RESPONSE --> If C=2pi*r and C=14pi m, then set these equal to each other and solve. 14pi = 2pi*r. Divide pi out: 14 = 2r. Divide the 2 out: 7 = r. Now find the area by using A = pi*r^2. A=pi*(7)^2 = 49pi m^2. confidence assessment: 2
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15:04:20 We know that A = pi r^2. We can find the area if we know the radius r. We therefore attempt to use the given information to find r. We know that circumference and radius are related by C = 2 pi r. Solving for r we obtain r = C / (2 pi). In this case we find that r = 14 pi m / (2 pi) = (14/2) * (pi/pi) m = 7 * 1 m = 7 m. We use this to find the area A = pi * (7 m)^2 = 49 pi m^2.
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RESPONSE --> Ok. self critique assessment: 3
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15:08:19 `q011. What is the radius of circle whose area is 78 square meters?
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RESPONSE --> We know A=pi*r^2 and A=78m^2, so set equal and solve: 78m^2 = pi*r^2. Divide by pi: 24.828 = r^2 Square root: 4.98m = r. So the radius is about 4.98m. confidence assessment: 2
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15:08:47 Knowing that A = pi r^2 we solve for r. We first divide both sides by pi to obtain A / pi = r^2. We then reverse the sides and take the square root of both sides, obtaining r = sqrt( A / pi ). Note that strictly speaking the solution to r^2 = A / pi is r = +-sqrt( A / pi ), meaning + sqrt( A / pi) or - sqrt(A / pi). However knowing that r and A are both positive quantities, we can reject the negative solution. Now we substitute A = 78 m^2 to obtain r = sqrt( 78 m^2 / pi) = sqrt(78 / pi) m.{} Approximating this quantity to 2 significant figures we obtain r = 5.0 m.
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RESPONSE --> Pretty close. I didn't round that much. self critique assessment: 2
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15:09:23 `q012. Summary Question 1: How do we visualize the area of a rectangle?
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RESPONSE --> Think about it in terms of lots of little tiny blocks which make up a large block. These little blocks are measureable, such as ft^2. confidence assessment: 2
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15:10:10 We visualize the rectangle being covered by rows of 1-unit squares. We multiply the number of squares in a row by the number of rows. So the area is A = L * W.
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RESPONSE --> I missed the formula and application a bit. self critique assessment: 2
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15:11:32 `q013. Summary Question 2: How do we visualize the area of a right triangle?
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RESPONSE --> To visualize the area of a right triangle, think of a square with the same length sides as the right triangle. Then cut that square in half from one corner to the opposite corner and there is the right triangle. The formula is A=1/2(b*h). confidence assessment: 2
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15:11:43 We visualize two identical right triangles being joined along their common hypotenuse to form a rectangle whose length is equal to the base of the triangle and whose width is equal to the altitude of the triangle. The area of the rectangle is b * h, so the area of each triangle is 1/2 * b * h.
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RESPONSE --> Pretty close. self critique assessment: 2
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15:13:05 `q014. Summary Question 3: How do we calculate the area of a parallelogram?
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RESPONSE --> To calculate the area of a parallelogram, remember that all the sides are parallel and therefore the two ends can be cut off to form another square. This means that the base and height can simply be multiplied together like a normal square and the correct area will result. Formula: A=L*W. confidence assessment: 3
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15:13:16 The area of a parallelogram is equal to the product of its base and its altitude. The altitude is measured perpendicular to the base.
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RESPONSE --> Ok. self critique assessment: 3
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15:16:49 `q015. Summary Question 4: How do we calculate the area of a trapezoid?
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RESPONSE --> To calculate the area of a trapeziod, we need to find the average height of the two sides which are not parallel. We then multiply that with the base and that will result in the area of the trapezoid. The formula is: A=base*((height1 + height2)/2) confidence assessment: 2
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15:16:57 We think of the trapezoid being oriented so that its two parallel sides are vertical, and we multiply the average altitude by the width.
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RESPONSE --> Ok. self critique assessment: 3
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15:17:44 `q016. Summary Question 5: How do we calculate the area of a circle?
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RESPONSE --> To calculate the area of a circle, use the formula A=pi*r^2. confidence assessment: 2
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15:17:51 We use the formula A = pi r^2, where r is the radius of the circle.
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RESPONSE --> Yep. self critique assessment: 3
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15:19:01 `q017. Summary Question 6: How do we calculate the circumference of a circle? How can we easily avoid confusing this formula with that for the area of the circle?
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RESPONSE --> Circumference can be found with the formula C=2pi*r. To keep this separate from the Area formula, remember the units each comes in. The units for the area measurement will always be squared, while the units for the circumference will not. confidence assessment: 2
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15:19:10 We use the formula C = 2 pi r. The formula for the area involves r^2, which will give us squared units of the radius. Circumference is not measured in squared units.
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RESPONSE --> Ok. self critique assessment: 3
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15:21:30 `q018. Explain how you have organized your knowledge of the principles illustrated by the exercises in this assignment.
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RESPONSE --> This assignment has covered some basic area and length assignments and so has been a good refresher. I am not sure how if I did any further organization of my knowledge of these principles in this assignment. confidence assessment: 1
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TȷNƩЏҔ{Ly assignment #002 002. Volumes qa areas volumes misc 06-01-2007
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15:35:24 `q001. There are 9 questions and 4 summary questions in this assignment. What is the volume of a rectangular solid whose dimensions are exactly 3 cm by 5 cm by 7 cm?
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RESPONSE --> Simply multiply the length by the width by the height. V = L*W*H. V = 3*5*7 = 105cm^3. confidence assessment: 2
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15:37:32 If we orient this object so that its 3 cm dimension is its 'height', then it will be 'resting' on a rectangular base whose dimension are 5 cm by 7 cm. This base can be divided into 5 rows each consisting of 7 squares, each 1 meter by 1 meter. There will therefore be 5 * 7 = 35 such squares, showing us that the area of the base is 35 m^2. Above each of these base squares the object rises to a distance of 3 meters, forming a small rectangular tower. Each such tower can be divided into 3 cubical blocks, each having dimension 1 meter by 1 meter by 1 meter. The volume of each 1-meter cube is 1 m * 1 m * 1 m = 1 m^3, also expressed as 1 cubic meter. So each small 'tower' has volume 3 m^3. The object can be divided into 35 such 'towers'. So the total volume is 35 * 3 m^3 = 105 m^3. This construction shows us why the volume of a rectangular solid is equal to the area of the base (in this example the 35 m^2 of the base) and the altitude (in this case 3 meters). The volume of any rectangular solid is therefore V = A * h, where A is the area of the base and h the altitude. This is sometimes expressed as V = L * W * h, where L and W are the length and width of the base. However the relationship V = A * h applies to a much broader class of objects than just rectangular solids, and V = A * h is a more powerful idea than V = L * W * h. Remember both, but remember also that V = A * h is the more important.
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RESPONSE --> Never thought of it as V=A*h before. Sugar cubes! self critique assessment: 2
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15:38:21 `q002. What is the volume of a rectangular solid whose base area is 48 square meters and whose altitude is 2 meters?
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RESPONSE --> V=A*h. Multiply the area of the base by the height. V = 48m^2 * 2 = 96m^3. confidence assessment: 2
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15:38:29 Using the idea that V = A * h we find that the volume of this solid is V = A * h = 48 m^2 * 2 m = 96 m^3. Note that m * m^2 means m * (m * m) = m * m * m = m^2.
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RESPONSE --> Ok. self critique assessment: 3
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15:43:15 `q003. What is the volume of a uniform cylinder whose base area is 20 square meters and whose altitude is 40 meters?
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RESPONSE --> The volume of a cylinder can be found with the formula V=pi*r^2*h, which is the area of the circle multiplied by the height. By using V=A*h, the area of the cylinder can be found as well. V=20m^2 * 40 = 800m^3. confidence assessment: 2
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15:43:24 V = A * h applies to uniform cylinders as well as to rectangular solids. We are given the altitude h and the base area A so we conclude that V = A * h = 20 m^2 * 40 m = 800 m^3. The relationship V = A * h applies to any solid object whose cross-sectional area A is constant. This is the case for uniform cylinders and uniform prisms.
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RESPONSE --> That works. self critique assessment: 3
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15:45:03 `q004. What is the volume of a uniform cylinder whose base has radius 5 cm and whose altitude is 30 cm?
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RESPONSE --> Here we use that formula I listed a bit ago, V=pi*r^2*h. V = pi*(5)^2*30 V = 750pi m^3 or 2356 m^3 (rounded). confidence assessment: 2
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15:51:12 The cylinder is uniform, which means that its cross-sectional area is constant. So the relationship V = A * h applies. The cross-sectional area A is the area of a circle of radius 5 cm, so we see that A = pi r^2 = pi ( 5 cm)^2 = 25 pi cm^2. Since the altitude is 30 cm the volume is therefore V = A * h = 25 pi cm^2 * 30 cm = 750 pi cm^3. Note that the common formula for the volume of a uniform cylinder is V = pi r^2 h. However this is just an instance of the formula V = A * h, since the cross-sectional area A of the uniform cylinder is pi r^2. Rather than having to carry around the formula V = pi r^2 h, it's more efficient to remember V = A * h and to apply the well-known formula A = pi r^2 for the area of a circle.
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RESPONSE --> Ah ha. self critique assessment: 3
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w}nΡ^ assignment #001 001. Rates qa rates 06-01-2007 xʍ_ؖՉ̌ assignment #002 002. Volumes qa areas volumes misc 06-01-2007
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20:40:02 `q005. Estimate the dimensions of a metal can containing food. What is its volume, as indicated by your estimates?
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RESPONSE --> The diameter of the can is 7.5cm and the height is 9.5cm. To find the area, we find the radius which is 1/2 the diameter or 3.75cm. A=pi*r^2 A=pi*(3.75)^2 A=14pi cm^2 To find the volume, we multiply height by area. V=A*h V=14pi*9.5 = 419.7cm^3. confidence assessment: 2
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20:40:37 People will commonly estimate the dimensions of a can of food in centimeters or in inches, though other units of measure are possible (e.g., millimeters, feet, meters, miles, km). Different cans have different dimensions, and your estimate will depend a lot on what can you are using. A typical can might have a circular cross-section with diameter 3 inches and altitude 5 inches. This can would have volume V = A * h, where A is the area of the cross-section. The diameter of the cross-section is 3 inches so its radius will be 3/2 in.. The cross-sectional area is therefore A = pi r^2 = pi * (3/2 in)^2 = 9 pi / 4 in^2 and its volume is V = A * h = (9 pi / 4) in^2 * 5 in = 45 pi / 4 in^3. Approximating, this comes out to around 35 in^3. Another can around the same size might have diameter 8 cm and height 14 cm, giving it cross-sectional area A = pi ( 4 cm)^2 = 16 pi cm^2 and volume V = A * h = 16 pi cm^2 * 14 cm = 224 pi cm^2.
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RESPONSE --> I think I did that. self critique assessment: 3
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20:55:37 `q006. What is the volume of a pyramid whose base area is 50 square cm and whose altitude is 60 cm?
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RESPONSE --> The formula for the volume of a pyramid is V=1/3*A*h. V=1/3*50*60 = 1000cm^3. confidence assessment: 2
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20:56:04 We can't use the V = A * h idea for a pyramid because the thing doesn't have a constant cross-sectional area--from base to apex the cross-sections get smaller and smaller. It turns out that there is a way to cut up and reassemble a pyramid to show that its volume is exactly 1/3 that of a rectangular solid with base area A and altitude h. Think of putting the pyramid in a box having the same altitude as the pyramid, with the base of the pyramid just covering the bottom of the box. The apex (the point) of the pyramid will just touch the top of the box. The pyramid occupies exactly 1/3 the volume of that box. So the volume of the pyramid is V = 1/3 * A * h. The base area A is 30 cm^2 and the altitude is 60 cm so we have V = 1/3 * 50 cm^2 * 60 cm = 1000 cm^3.
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RESPONSE --> Ok. self critique assessment: 3
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20:58:26 `q007. What is the volume of a cone whose base area is 20 square meters and whose altitude is 9 meters?
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RESPONSE --> The formula for the volume of a cone is V=1/3*A*h. V=1/3*20*9 = 60m^3. confidence assessment: 2
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20:59:25 Just as the volume of a pyramid is 1/3 the volume of the 'box' that contains it, the volume of a cone is 1/3 the volume of the cylinder that contains it. Specifically, the cylinder that contains the cone has the base of the cone as its base and matches the altitude of the cone. So the volume of the cone is 1/3 A * h, where A is the area of the base and h is the altitude of the cone. In this case the base area and altitude are given, so the volume of the cone is V = 1/3 A * h = 1/3 * 20 m^2 * 9 m = 60 m^3.
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RESPONSE --> Ok. self critique assessment: 3
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21:01:18 `q008. What is a volume of a sphere whose radius is 4 meters?
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RESPONSE --> The formula for the volume of a sphere is V=4/3pi*r^3. V=4/3*pi*4^3 = 85.33pi m^3. confidence assessment: 2
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21:01:27 The volume of a sphere is V = 4/3 pi r^3, where r is the radius of the sphere. In this case r = 4 m so V = 4/3 pi * (4 m)^3 = 4/3 pi * 4^3 m^3 = 256/3 pi m^3.
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RESPONSE --> Ok. self critique assessment: 3
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21:03:20 `q009. What is the volume of a planet whose diameter is 14,000 km?
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RESPONSE --> Diameter is equal to 2r, so the radius of the planet is equal to 7,000 km. Therefore the volume is: V=4/3pi*(7000)^3 = 4.57e11*pi m^3. confidence assessment: 2
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21:04:03 The planet is presumably a sphere, so to the extent that this is so the volume of this planet is V = 4/3 pi r^3, where r is the radius of the planet. The diameter of the planet is 14,000 km so the radius is half this, or 7,000 km. It follows that the volume of the planet is V = 4/3 pi r^3 = 4/3 pi * (7,000 km)^3 = 4/3 pi * 343,000,000,000 km^3 = 1,372,000,000,000 / 3 * pi km^3. This result can be approximated to an appropriate number of significant figures.
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RESPONSE --> I just had it in a more reduced form. self critique assessment: 2
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21:05:41 `q010. Summary Question 1: What basic principle do we apply to find the volume of a uniform cylinder of known dimensions?
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RESPONSE --> We use the same idea as we use in calculating the volume of a cube: Volume is equal to the area of the base multiplied by the height. confidence assessment: 2
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21:05:54 The principle is that when the cross-section of an object is constant, its volume is V = A * h, where A is the cross-sectional area and h the altitude. Altitude is measure perpendicular to the cross-section.
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RESPONSE --> I forgot the formula. self critique assessment: 2
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21:07:47 `q011. Summary Question 2: What basic principle do we apply to find the volume of a pyramid or a cone?
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RESPONSE --> We use the same idea of volume being equal to the base area multiplied by the height (V=A*h), but we have to divide it by three since the pyramid/cone is a third of the size of the cube/cylinder. Therefore the formula is V=1/3*A*h. confidence assessment: 2
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21:07:54 The volumes of these solids are each 1/3 the volume of the enclosing figure. Each volume can be expressed as V = 1/3 A * h, where A is the area of the base and h the altitude as measured perpendicular to the base.
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RESPONSE --> Ok. self critique assessment: 3
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21:08:38 `q012. Summary Question 3: What is the formula for the volume of a sphere?
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RESPONSE --> The formula for the volume of a sphere is V=4/3*pi*r^3. confidence assessment: 2
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21:08:46 The volume of a sphere is V = 4/3 pi r^3, where r is the radius of the sphere.
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RESPONSE --> Ok. self critique assessment: 3
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21:09:39 `q013. Explain how you have organized your knowledge of the principles illustrated by the exercises in this assignment.
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RESPONSE --> Again, I am not quite sure. I did more work trying to reason out exactly how each one worked together, but other than that, I don't think I did much organizing. confidence assessment: 1
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yжZU assignment #003 003. Misc: Surface Area, Pythagorean Theorem, Density qa areas volumes misc 06-01-2007
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21:25:20 `q001. There are 10 questions and 5 summary questions in this assignment. What is surface area of a rectangular solid whose dimensions are 3 meters by 4 meters by 6 meters?
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RESPONSE --> The area of a rectangular solid is simply the area of each side of the rectangle added together. The simple way is this: V = 2ab + 2bc + 2ac. V = 2(3*4) + 2(4*6) + 2(3*6) = 108m^2. confidence assessment: 2
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21:25:31 A rectangular solid has six faces (top, bottom, front, back, left side, right side if you're facing it). The pairs top and bottom, right and left sides, and front-back have identical areas. This solid therefore has two faces with each of the following dimensions: 3 m by 4 m, 3 m by 6 m and 4 m by 6 m, areas 12 m^2, 18 m^2 and 24 m^2. Total area is 2 * 12 m^2 + 2 * 18 m^2 + 2 * 24 m^2 = 108 m^2.
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RESPONSE --> Ok. self critique assessment: 2
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21:36:50 `q002. What is the surface area of the curved sides of a cylinder whose radius is five meters and whose altitude is 12 meters? If the cylinder is closed what is its total surface area?
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RESPONSE --> If we know the radius of the cylinder and we are trying to find the area of the curved area, then we need to first find circumference. C=2pi*r = 10pi. Then multiply that by the altitude of the cylinder to find the area of the curved section: A1 = 10pi*12 = 120pi. To find the total surface area, add the area of the curved section to twice the area of the top (or bottom): A2 = pi*5^2 = 25pi. 2(25pi) + 120pi = 170pi m^2 total surface area. confidence assessment: 2
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21:36:59 The circumference of this cylinder is 2 pi r = 2 pi * 5 m = 10 pi m. If the cylinder was cut by a straight line running up its curved face then unrolled it would form a rectangle whose length and width would be the altitude and the circumference. The area of the curved side is therefore A = circumference * altitude = 10 pi m * 12 m = 120 pi m^2. If the cylinder is closed then it has a top and a bottom, each a circle of radius 5 m with resulting area A = pi r^2 = pi * (5 m)^2 = 25 pi m^2. The total area would then be total area = area of sides + 2 * area of base = 120 pi m^2 + 2 * 25 pi m^2 = 170 pi m^2.
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RESPONSE --> Ok. confidence assessment: 2
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21:43:47 `q003. What is surface area of a sphere of diameter three cm?
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RESPONSE --> The formula is A=4pi*r^2, so the surface area of the sphere is: A=4pi*(3)^2 = 36pi. confidence assessment: 2
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21:44:18 The surface area of a sphere of radius r is A = 4 pi r^2. This sphere has radius 3 cm / 2, and therefore has surface area A = 4 pi r^2 = 4 pi * (3/2 cm)^2 = 9 pi cm^2.
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RESPONSE --> I forgot to divide the diameter in half. self critique assessment: 2
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21:48:13 `q004. What is hypotenuse of a right triangle whose legs are 5 meters and 9 meters?
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RESPONSE --> To find the hypotenuse of a right triangle, use the formula c^2 = a^2+b^2. Then simply find the square root. C = sqrt(5^2+9^2) = sqrt(106) = 10.3. confidence assessment: 2
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21:49:12 `q005. If the hypotenuse of a right triangle has length 6 meters and one of its legs has length 4 meters what is the length of the other leg?
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RESPONSE --> Forgot to put the units on. confidence assessment: 2
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21:54:39 If c is the hypotenuse and a and b the legs, we know by the Pythagorean Theorem that c^2 = a^2 + b^2, so that a^2 = c^2 - b^2. Knowing the hypotenuse c = 6 m and the side b = 4 m we therefore find the unknown leg: a = sqrt( c^2 - b^2) = sqrt( (6 m)^2 - (4 m)^2 ) = sqrt(36 m^2 - 16 m^2) = sqrt(20 m^2) = sqrt(20) * sqrt(m^2) = 2 sqrt(5) m, or approximately 4.4 m.
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RESPONSE --> Did I miss something? Somehow I missed the question, though only the question was recorded in the text box. Anyway, here is my answer to the question: If we have C and A and need to find B, then we use the equation c^2 = a^2 + b^2. 6^2 = 4^2 + b^2 36 - 16 = b^2 b = sqrt(20) b = 2sqrt(5) m or 4.47 m. self critique assessment: 2
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21:58:22 `q006. If a rectangular solid made of a uniform, homogeneous material has dimensions 4 cm by 7 cm by 12 cm and if its mass is 700 grams then what is its density in grams per cubic cm?
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RESPONSE --> First we need to find number of cubic cm in the cube: 4*7*12 = 336cm^3. Then divide the grams by the cubic cm to find the grams per cm^3: 700 / 336cm^3 = 2.08 g/cm^3. confidence assessment: 2
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21:58:40 The volume of this solid is 4 cm * 7 cm * 12 cm = 336 cm^3. Its density in grams per cm^3 is the number of grams in each cm^3. We find this quantity by dividing the number of grams by the number of cm^3. We find that density = 700 grams / (336 cm^3) = 2.06 grams / cm^3. Note that the solid was said to be uniform and homogeneous, meaning that it's all made of the same material, which is uniformly distributed. So each cm^3 does indeed have a mass of 2.06 grams. Had we not known that the material was uniform and homogeneous we could have said that the average density is 2.06 grams / cm^3, but not that the density is 2.06 grams / cm^3 (the object could be made of two separate substances, one with density less than 2.06 grams / cm^3 and the other with density greater than 2.06 g / cm^3, in appropriate proportions; neither substance would have density 2.06 g / cm^3, but the average density could be 2.06 g / cm^3).
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RESPONSE --> Ah, averages... self critique assessment: 2
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22:05:56 `q007. What is the mass of a sphere of radius 4 meters if its average density is 3,000 kg/cubic meter?
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RESPONSE --> First find the cubic m of the sphere: V = 4/3pi*r^3 V = 4/3pi*(4)^3 V = 85.33pi m^3. Now multiply the volume of the sphere by the average density of the sphere: 85.33pi m^3 * 3000 kg/m^3 = 256,000pi kg or 804,247 kg. confidence assessment: 2
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22:06:13 A average density of 3000 kg / cubic meter implies that, at least on the average, every cubic meter has a mass of 3000 kg. So to find the mass of the sphere we multiply the number of cubic meters by 3000 kg. The volume of a sphere of radius 4 meters is 4/3 pi r^3 = 4/3 * pi (4m)^3 = 256/3 * pi m^3. So the mass of this sphere is mass = density * volume = 256 / 3 * pi m^3 * 3000 kg / m^3 = 256,000 * pi kg. This result can be approximated to an appropriate number of significant figures.
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RESPONSE --> Ok. self critique assessment: 3
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22:11:42 `q008. If we build a an object out of two pieces of material, one having a volume of 6 cm^3 at a density of 4 grams per cm^3 and another with a volume of 10 cm^3 at a density of 2 grams per cm^3 then what is the average density of this object?
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RESPONSE --> Add together the volumes and add together the densities: Volumes: 6cm^3 + 10cm^3 = 16cm^3. Densities: 6*4+10*2 = 44g. To find the average density, divide the grams by the cm^3: 44/16 = 2.75 g/cm^3. 2.75 g/cm^3 is the average density of the object. confidence assessment: 2
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22:11:49 The first piece has a mass of 4 grams / cm^3 * 6 cm^3 = 24 grams. The second has a mass of 2 grams / cm^3 * 10 cm^3 = 20 grams. So the total mass is 24 grams + 20 grams = 44 grams. The average density of this object is average density = total mass / total volume = (24 grams + 20 grams) / (6 cm^3 + 10 cm^3) = 44 grams / (16 cm^3) = 2.75 grams / cm^3.
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RESPONSE --> Ok. self critique assessment: 3
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22:19:42 `q009. In a large box of dimension 2 meters by 3 meters by 5 meters we place 27 cubic meters of sand whose density is 2100 kg/cubic meter, surrounding a total of three cubic meters of cannon balls whose density is 8,000 kg per cubic meter. What is the average density of the material in the box?
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RESPONSE --> I assume that the box itself has no density. First find the cubic meters of the box itself: 2*3*5 = 30m^3, which is also the amount of cubic meters of material in the box. Now we need to know the total densities of the sand: 27*2100 = 56,700kg. The cannon balls: 8000*3 = 24,000kg. Now add the two weights together and divide by the total cubic meters: (56700 + 24000) / 30 = 2,690 kg/m^3 average density in the box. confidence assessment: 2
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22:20:15 We find the average density from the total mass and the total volume. The mass of the sand is 27 m^3 * 2100 kg / m^3 = 56,700 kg. The mass of the cannonballs is 3 m^3 * 8,000 kg / m^3 = 24,000 kg. The average density is therefore average density = total mass / total volume = (56,700 kg + 24,000 kg) / (27 m^3 + 3 m^3) = 80,700 kg / (30 m^3) = 2,700 kg / m^3, approx..
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RESPONSE --> Ok. self critique assessment: 3
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22:23:33 `q010. How many cubic meters of oil are there in an oil slick which covers 1,700,000 square meters (between 1/2 and 1 square mile) to an average depth of .015 meters? If the density of the oil is 860 kg/cubic meter the what is the mass of the oil slick?
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RESPONSE --> To find the cubic meters of oil, multiply the square meters of the oil by the average depth of the slick: 1,700,000 * .015 = 25,500m^3. To find the mass, multiply the cubic meters of the oil slick by the density of the slick: 25,500 * 860 = 21,930,000kg. confidence assessment: 2
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22:25:26 The volume of the slick is V = A * h, where A is the area of the slick and h the thickness. This is the same principle used to find the volume of a cylinder or a rectangular solid. We see that the volume is V = A * h = 1,700,000 m^2 * .015 m = 25,500 m^3. The mass of the slick is therefore mass = density * volume = 860 kg / m^3 * 24,400 m^3 = 2,193,000 kg. This result should be rounded according to the number of significant figures in the given information.
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RESPONSE --> Hmm, my numbers are oddly different. For some reason, multiplying out what is here (860 * 24400) equals 20,984,000 kg, not 2,193,000 kg. self critique assessment: 3
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22:29:17 `q011. Summary Question 1: How do we find the surface area of a cylinder?
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RESPONSE --> To find the surface area of a cylinder, we need to find the area of the top, the bottom, and the lateral (side) area. To find the side area, we find the circumference of the top then multiply that by the height. We then add that to twice the surface area of the top and the result is the surface area of the cylinder. confidence assessment: 2
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22:29:44 The curved surface of the cylinder can be 'unrolled' to form a rectangle whose dimensions are equal to the circumference and the altitude of the cylinder, so the curved surface has volume Acurved = circumference * altitude = 2 pi r * h, where r is the radius and h the altitude. The top and bottom of the cylinder are both circles of radius r, each with resulting area pi r^2. {]The total surface area is therefore Acylinder = 2 pi r h + 2 pi r^2.
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RESPONSE --> I just missed the formula. self critique assessment: 2
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22:30:31 `q012. Summary Question 2: What is the formula for the surface area of a sphere?
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RESPONSE --> The formula of the surface area of a sphere is: A = 4pi*r^2. confidence assessment: 3
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22:30:38 The surface area of a sphere is A = 4 pi r^2, where r is the radius of the sphere.
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RESPONSE --> Ok. self critique assessment: 3
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22:31:26 `q013. Summary Question 3: What is the meaning of the term 'density'.
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RESPONSE --> Density measures just how much stuff there is in a certain amount of cubic space. confidence assessment: 2
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22:31:55 The average density of an object is its mass per unit of volume, calculated by dividing its total mass by its total volume. If the object is uniform and homogeneous then its density is constant and we can speak of its 'density' as opposed to its 'average density'
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RESPONSE --> I missed the math part in which I should have mentioned that the density is the mass divided by the volume. self critique assessment: 2
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22:33:10 `q014. Summary Question 4: If we know average density and mass, how can we find volume?
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RESPONSE --> If we know the average density and mass, then we can find the volume through this relationship: mass / volume = density We can then rearrange it to solve for volume: mass / density = volume. confidence assessment: 2
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22:33:18 Since mass = ave density * volume, it follows by simple algebra that volume = mass / ave density.
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RESPONSE --> Ok. self critique assessment: 3
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22:34:15 `q015. Explain how you have organized your knowledge of the principles illustrated by the exercises in this assignment.
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RESPONSE --> More memory refreshing and slight reorganization. I got to work out the logical connections between some of the mathematical relationships. confidence assessment: 2
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