#$&*
course Phy 201
1. An inch is 2.54 centimeters. How can you use this information along with common knowledge to find the following?The number of centimeters in a foot.
There are 30.48cm in one foot, I found this by multiplying 2.54 by 12 because there are 12 inches in one foot.
#$&*
The number of feet in a meter.
There are 3.28 feet in one meter.
#$&*
The number of meters in a mile.
There are 1609.76 meters in one mile I found this by taking the number of feet in a mile (5280) and dividing 3.28 into that.
#$&*
The number of nanometers in a mil (a mil is 1/1000 of an inch).
There are 25,400 nanometers in one mil.
#$&*
2. A cube 10 centimeters on a side would hold 1 liter of water. A cube 1 centimeter on a side would hold 1 milliliter of water. Show how this information along with common knowledge, allows you to answer the following questions:
How many milliliters are in a liter?
There are 1000 milliliters in 1 liter.
#$&*
How many milliliters are there in a cubic meter?
There are 1,000,000 mL in one cubic meter.
#$&*
How many liters are there in a cubic kilometer?
There are 1,000,000,000,000L in one cubic kilometer.
#$&*
How many cubic meters are there in a cubic mile?
There are 4,168,181,825 cubic meters in one cubic mile.
#$&*
3. Steel has a density between 7 grams / cm^3 and 8 grams / cm^3. The larger steel balls we use in the lab have diameter 1 inch. Some of the smaller balls have diameter 1/2 inch.
What therefore is the mass of one of the larger balls?
****
#$&*
What would the mass of the smaller ball be as a fraction of the mass of the larger ball?
****
#$&*
@& These balls are spheres of given radii.
Each radius can be expressed in cm. Then use the formula for the volume of a sphere, etc.*@
4. Using common knowledge and the fact that 1 inch = 2.54 centimeters, express a mile/hour in centimeters / second.
1MPH would equal 44.7cm/s.
#$&*
5. Using your measurements of a domino, find the following:
The ratio of its length to its width.
The ratio of a dominos length to its width is 1:2. Because I found the length to be 5cm and the width to be 2.5cm.
#$&*
The ratio of its width to its thickness.
The ratio of its width to its thickness would be about 1:4.
#$&*
The volume of a domino.
The volume of the domino that I measured would have been 8.75cm^3.
#$&*
The percent uncertainty in your results, according to your estimates of the uncertainty in your measurements.
The percent uncertainty in my results was about 20% because of a few factors such as the ruler used may not have been exact in its measurements and some of the results such as the thickness may have been a little off.
#$&*
6. Estimate how many of the large steel balls would fit into a drinking cup. Then based on your estimate and the fact that the small green BB's in the lab have diameters of 6 millimeters, estimate how many of those BB's would fit into a cup.
I would estimate that 20 of the steel balls would fit in a cup and 160 of the small bb’s would fit in a cup.
@& If the small bb's were each half the diameter of the ball then the volume of a ball would be the same as that of 8 bb's, and your estimate of the number of bb's would correlate well with the number of balls.
However the bb's have only about 1/4 the diameter of the balls.*@
#$&*
7. Estimate the volume and mass of a single Cheerio. As a point of reference, an average almond has a mass of about a gram.
The volume of a cheerio is about .3cm^3 and the mass is about .25g.
#$&*
If half the mass of the Cheerio consists of carbohydrates, and if a gram of carbohydrate has a food energy of about 4 000 Joules, then what is your estimate of the food energy of a single Cheerio?
I would estimate that the food energy in 1 cheerio to be about 1000 Joules.
#$&*
8. Estimate the number of grains of typical desert sand in a liter. Then estimate the number of liters of sand on a 100-meter stretch of your favorite beach.
I would estimate the number of grains of desert sand in 1 liter to be + or - 200,000 and in the 100m stretch of beach to be + or - 100,000 because there is about 1000 liters in cubic meter.
#$&*
Compare the number of grains of sand with the number of stars in our galaxy, that number estimated to be about 100 billion.
I would say that ratio of grains of sand to stars in the galaxy would be astronomical possibly in the 100’s to 1.
@& 200 000 grains per liter and 100 000 liters on the beach would imply 2 000 000 000 grains of sand on the bech.
Way more stars than that.*@
#$&*
Compare the number of grains with the number of stars in the universe, which contains over 100 billion galaxies whose average size is about the same as ours.
I would think that there might just be a few more stars now but I am not completely sure, the numbers would be fairly close.
#$&*
9. Water has a density of 1 gram / cm^3.
Using this information how would you reason out the density of water in kilograms / meter^3?
The way I see to do this is divide by 1000 since there are 1000g in 1kg and somehow divide by 100 also because a cm is 1/100th the length of a meter.
@& A cm is 1/100 of a meter, but a 1 cm cube is way less than 1/100 of a 1-meter cube.*@
#$&*
10. A rubber ball of diameter 25 cm is dropped on the floor from a height of 1 meter, and bounces back up to a height of 70 cm.
What is the ball's speed when it first contacts the floor, and what is its speed when it first loses contact with the floor on its rebound?
The balls speed when it hits the floor is 9.8m/s^2 and when it first loses contact with the floor it going around .75m/s^2.
@& Speed isn't measure in m/s^2.
You know how far it drops, you know it starts from rest and you know its acceleration. So you can find its velocity when it reaches the floor.*@
#$&*
Make a reasonable estimate of how far the center of the ball moves as it compresses before starting its rebound.
What do you think is its average acceleration during its compression?
How long do you think it takes to compress?
I think the center of the ball moves around 5 cm , the average acceleration is 9.8m/s^2 and I think it takes about .2s to compress.
@& At its final speed how long would it take the ball to move a distance equal to its diameter?
How would this compare with the compression time you would expect?*@
#$&*
How much KE does it lose, per gram of its mass, during the compression?
I am not exactly sure how much KE it loses but reasoning the events out I would think it lose all of it during the compression and build potential and change that potential into kinetic.
@& Right idea.
If you know how fast it's moving when it starts to compress you can figure out its KE per gram of mass.*@
#$&*
How much KE does it gain, per gram of its mass, as it decompresses?
****
#$&*
How much momentum does it have, per gram of its mass, just before it first reaches the floor?
****
#$&*
How much momentum does it have, per gram of its mass, just after it first leaves the floor on its way up?
****
#$&*
11. I'm pulling out a parking place on the side of the street, in a pickup truck with mass 1700 kg (including the contents of the truck, which among other things includes me).
I wait for a car to pass before pulling out, then pull out while accelerating at .5 m/s^2. At the instant I pull out, the other car is 20 meters past me and moving at 10 meters / second. If that car's speed and my acceleration both remain constant, then
How long will it take me to match its speed?
It will take you 20 seconds to reach the same speed as that car.
#$&*
How far behind will I be at that instant?
You will be at the same spot as that car is.
@& That car has been moving faster than I have for the entire 10 seconds, and it started out 20 m ahead of me. I won't start catching up until after I've matched his speed.
How far did I travel in the 20 seconds? How far did he travel?*@
#$&*
How much longer will it take me to catch up, and how fast will I be going when I do?
It will take you 20 seconds to catch up to the other car and you will be going the same speed as the other car.
#$&*
How much work will the net force on my truck have done by the time I catch the other car?
The net force of your truck will be 850N.
#$&*
If I hit my brakes when I'm 20 meters behind that car, then how much force will be required to slow me down sufficiently that I don't catch up with the car? How does this force compare with the weight of my truck?
I am not sure how to calculate that force but I know that it will have to be substantially greater than the 850N and it will also have to be greater than the mass of your truck to slow it down quickly.
#$&*
12. A ball is dropped from rest from a window, and passes another lower window in .32 seconds. That window is 1.4 meters high. From what height was the ball dropped?
The ball was dropped from a height of 1.9m.
#$&*
13. To maintain a speed of 1 meter / second a swimmer must generate 200 watts of power. The swimmer breathes once every stroke and covers a distance of 2 meters per stroke. To sustain this pace the swimmer must inhale enough air with every stroke to support the production of the necessary energy. How much energy must be produced in for each breath?
The swimmer must produce 400 watts with every breath that is taken.
#
@& Good start on these.
Go ahead and revise at least the questions I gave you notes on.
&#Please see my notes and, unless my notes indicate that revision is optional, submit a copy of this document with revisions and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.
If my notes indicate that revision is optional, use your own judgement as to whether a revision will benefit you. &#
*@