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course Phy 121
10/1 8am
ph1 query 1
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Question: `qExplain in your own words how the standard deviation of a set of numbers is calculated.
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Your solution:
In order to find the standard deviation of a sample set of numbers, the mean deviations from the mean interval of the sample set must first be calculated. Next you take the absolute difference between each of the intervals within the sample set and the mean interval. The differences found are the deviations of the intervals from the mean of all the intervals. Each of these deviations is squared. All of the squared deviations are averaged. If the data set is less than 30 samples, the average is found not by adding all the squared deviations and dividing by the number of deviations, but rather divided by one number less than the number of samples in the set. The resulting factor is the avg. squared deviation. The Standard Deviation is the square root of the average squared deviation.
confidence rating #$&*:3
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Question: State the given definition of the average rate of change of A with respect to B.
Briefly state what you think velocity is and how you think it is an example of a rate of change.
In reference to the definition of average rate of change, if you were to apply that definition to get an average velocity, what would you use for the A quantity and what would you use for the B quantity?
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Your solution:
The average rate of change of A with respect to B is defined as the change in A over or divided by the change in B. Velocity is the change of an object's position with respect to the change in (clock) time. I think velocity is an example of rate of change because it is the change of an object (A)'s position with respect to the change in clock time,(B).
confidence rating #$&*:3
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Given Solution:
A rate is a change in something divided by a change in something else.
This question concerns velocity, which is the rate of change of position: change in position divided by change in clock time. **
NOTE ON NOTATION
Students often quote a formula like v = d / t. It's best to avoid this formula completely.
The average velocity on an interval is defined as the average rate of change of position with respect to clock time. By the definition of average rate, then, the average velocity on the interval is v_ave = (change in position / change in clock time).
One reason we might not want to use v = d / t: The symbol d doesn't look like a change in anything, nor does the symbol t. Also it's very to read 'd' and 'distance' rather than 'displacement'.
Another reason: The symbol v doesn't distinguish between initial velocity, final velocity, average velocity, change in velocity and instantaneous velocity, all of which are important concepts that need to be associated with distinct symbols.
In this course we use `d to stand for the capital Greek symbol Delta, which universally indicates the change in a quantity. If we use d for distance, then the 'change in distance' would be denoted `dd. It's potentially confusing to have two different d's, with two different meanings, in the same expression.
We generally use s or x to stand for position, so `ds or `dx would stand for change in position. Change in clock time would be `dt. Thus
v_Ave = `ds / `dt
(or alternatively, if we use x for position, v_Ave = `dx / `dt).
With this notation we can tell that we are dividing change in position by change in clock time.
For University Physics students (calculus-based note):
If x is the position then velocity is dx/dt, the derivative of position with respect to clock time. This is the limiting value of the rate of change of position with respect to clock time. You need to think in these terms.
v stands for instantaneous velocity. v_Ave stands for the average velocity on an interval.
If you used d for position then you would have the formula v = dd / dt. The dd in the numerator doesn't make a lot of sense; one d indicates the infinitesimal change in the other d.
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Self-critique (if necessary):
Ok I see why it's important to differentiate between displacement and distance. ????One question I have is that in mathmatics, I've been taught that distance depends on time; time is generally notated on the x-axis of a graph. The v_Ave = 'ds / 'dt would be a bit confusing if x were substituted for s, or am I mixing definitions here?????
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Self-critique rating:2
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Question: Given average speed and time interval how do you find distance moved?
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Your solution:
Multiply the average speed by the known time interval to find the distance moved:
If the average speed is 10 m / sec and the known time interval is 60 sec, you multiply 10m/sec by 60 sec. and calculate a distance of 600 m.
confidence rating #$&*:3
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Given Solution:
** You multiply average speed * time interval to find distance moved.
For example, 50 miles / hour * 3 hours = 150 miles. **
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Self-critique (if necessary):
OK
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Self-critique rating:3
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Question: Given average speed and distance moved how do you find the corresponding time interval?
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Your solution:
'dt = 'ds / v_Ave OR, 'dt = 180 / 60 mph = 3 hours.
confidence rating #$&*:3
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Given Solution:
** time interval = distance / average speed. For example if we travel 100 miles at 50 mph it takes 2 hours--we divide the distance by the speed.
In symbols, if `ds = vAve * `dt then `dt = `ds/vAve.
Also note that (cm/s ) / s = cm/s^2, not sec, whereas cm / (cm/s) = cm * s / cm = s, as appropriate in a calculation of `dt. **
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Self-critique (if necessary):
OK
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Self-critique rating:3
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Question: Given time interval and distance moved how do you get average speed?
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Your solution:
v_Ave = 'ds / 'dt. If 'ds is 15m and 'dt is 5 sec, 15m / 5 sec = a v_Ave of 3 m/sec.
confidence rating #$&*:3
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Given Solution:
** Average speed = distance / change in clock time. This is the definition of average speed.
For example if we travel 300 miles in 5 hours we have been traveling at an average speed of 300 miles / 5 hours = 60 miles / hour. **
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Self-critique (if necessary):
OK
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Self-critique rating:3
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Question: A ball rolls from rest down a book, off that book and onto another book, where it picks up speed before rolling off the end of that book. Consider the interval that begins when the ball first encounters the second book, and ends when it rolls of the end of the book.
For this interval, place in order the quantities initial velocity (which we denote v_0), and final velocity (which we denote v_f), average velocity (which we denote v_Ave).
During this interval, the ball's velocity changes. It is possible for the change in its velocity to exceed the three quantities you just listed? Is it possible for all three of these quantities to exceed the change in the ball's velocity? Explain.
Note that the change in the ball's velocity is denoted `dv.
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Your solution:
????
I am a little uncertain as what is asked in the questions here. Am I to make up an initial velocity v_0 for when the ball hits the second book? I know the ball would not have a v_0 of 0 because it is already in motion. I know the v_Ave between v_0 and the middle of the second book would be less than the middle of the book and v_f from observation of the ball experiment in Asst. 0. I am uncertain as what ""It is possible for the change in its velocity to exceed the three quantities you just listed?is asking for????
@&
The question asks whether it is possible to arrange the books so that each of the given conditions holds.
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confidence rating #$&*:1
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Question: If the velocity at the beginning of an interval is 4 m/s and at the end of the interval it is 10 m/s, then what is the average of these velocities, and what is the change in velocity?
List the four quantities initial velocity, final velocity, average of initial and final velocities, and change in velocity, in order from least to greatest.
Give an example of positive initial and final velocities for which the order of the four quantities would be different.
For positive initial and final velocities, is it possible for the change in velocity to exceed the other three quanities?
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Your solution:
v_Ave is (4m/s + 10 m/s) / 2 (number of quantities) = 14m/s / 2 = 7m/sec. 'dv = 10 m/s - 4m/s= 6m/s. For this example, no I don't think it is possible as 6m/s ('dv) is 1m/s less than the v_Ave of 7m/s
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For the given situation the order of the quantities is fixed.
The second question here asks if you can describe a different situation in which the order would be different.
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confidence rating #$&*:3
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Question: If the position of an object changes by 5.2 meters, with an uncertainty of +-4%, during a time interval of 1.3 seconds, with an uncertainty of +-2%, then
What is the uncertainty in the change in position in meters>
What is the uncertainty in the time interval in seconds?
What is the average velocity of the object, and what do you think ia the uncertainty in the average velocity?
(this last question is required of University Physics students only, but other are welcome to answer): What is the percent uncertainty in the average velocity of the object, and what is the uncertainty as given in units of velocity?
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Your solution:
confidence rating #$&*:
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Self-critique (if necessary):
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Self-critique rating:
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Question: A ball rolls from rest down a book, off that book and onto another book, where it picks up speed before rolling off the end of that book. Consider the interval that begins when the ball first encounters the second book, and ends when it rolls of the end of the book.
For this interval, place in order the quantities initial velocity (which we denote v_0), and final velocity (which we denote v_f), average velocity (which we denote v_Ave).
During this interval, the ball's velocity changes. It is possible for the change in its velocity to exceed the three quantities you just listed? Is it possible for all three of these quantities to exceed the change in the ball's velocity? Explain.
Note that the change in the ball's velocity is denoted `dv.
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Your solution:
????
I am a little uncertain as what is asked in the questions here. Am I to make up an initial velocity v_0 for when the ball hits the second book? I know the ball would not have a v_0 of 0 because it is already in motion. I know the v_Ave between v_0 and the middle of the second book would be less than the middle of the book and v_f from observation of the ball experiment in Asst. 0. I am uncertain as what ""It is possible for the change in its velocity to exceed the three quantities you just listed?is asking for????
@&
The question asks whether it is possible to arrange the books so that each of the given conditions holds.
*@
confidence rating #$&*:1
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Question: If the velocity at the beginning of an interval is 4 m/s and at the end of the interval it is 10 m/s, then what is the average of these velocities, and what is the change in velocity?
List the four quantities initial velocity, final velocity, average of initial and final velocities, and change in velocity, in order from least to greatest.
Give an example of positive initial and final velocities for which the order of the four quantities would be different.
For positive initial and final velocities, is it possible for the change in velocity to exceed the other three quanities?
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Your solution:
v_Ave is (4m/s + 10 m/s) / 2 (number of quantities) = 14m/s / 2 = 7m/sec. 'dv = 10 m/s - 4m/s= 6m/s. For this example, no I don't think it is possible as 6m/s ('dv) is 1m/s less than the v_Ave of 7m/s
@&
For the given situation the order of the quantities is fixed.
The second question here asks if you can describe a different situation in which the order would be different.
*@
confidence rating #$&*:3
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Question: If the position of an object changes by 5.2 meters, with an uncertainty of +-4%, during a time interval of 1.3 seconds, with an uncertainty of +-2%, then
What is the uncertainty in the change in position in meters>
What is the uncertainty in the time interval in seconds?
What is the average velocity of the object, and what do you think ia the uncertainty in the average velocity?
(this last question is required of University Physics students only, but other are welcome to answer): What is the percent uncertainty in the average velocity of the object, and what is the uncertainty as given in units of velocity?
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Your solution:
confidence rating #$&*:
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Self-critique (if necessary):
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Self-critique rating:
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&#This looks good. See my notes. Let me know if you have any questions. &#