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course Phy 201

Physics I Class 111005You should use your text as a reference in solving the following, which are due next Wednesday:

Text-related problems:

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.

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2.54 cm per inch would equal when a foot equals 12 inches, it would be simple by taking 2.54 and multiplying it by 12 inches

Which equals 30.48 cm

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The number of feet in a meter.

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3.281

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The number of meters in a mile.

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5,280 feet in a mile /3.281 = 1609.27 meters

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The number of nanometers in a mil (a mil is 1/1000 of an inch).

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nano is 10^-9

so 1/1000 of an inch

1 cm equals .3937 inches so it would be .0003937

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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?

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1,000 milli means 1,000

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How many milliliters are there in a cubic meter?

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If there is 10 cm in 1 liter, then that means there is 100 milliliters in cubinc meter

@& A cube 10 cm on a side has volume 10 cm * 10 cm * 10 cm = 1000 cm^3.

A cubic meter is way more than 10 liters.*@

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How many liters are there in a cubic kilometer?

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100 liters in a kilometer

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How many cubic meters are there in a cubic mile?

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1609 meters

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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?

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V= 4/3(pie)r^3

V=.52 cm^3

P= m/v

7 g/cm^3=m/.52 cm^3= 3.64 grams

@& Good reasoning.

However the 1-inch diameter is 2.54 cm, so the radius is 1.27 cm, not .52 cm.*@

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What would the mass of the smaller ball be as a fraction of the mass of the larger ball?

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1/2

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4. Using common knowledge and the fact that 1 inch = 2.54 centimeters, express a mile/hour in centimeters / second.

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1 mile = 5280 feet = 63,360 inches= 160,934.4 cm

160,934.4 cm/ 3600 seconds

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5. Using your measurements of a domino, find the following:

The ratio of its length to its width.

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5:2.5

1:2

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The ratio of its width to its thickness.

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2.5:0.8

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The volume of a domino.

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V= lwh

5*2.5*.08

1cm^3

@& Good, but the width is .8 cm, not .08 cm.*@

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The percent uncertainty in your results, according to your estimates of the uncertainty in your measurements.

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+-2%

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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.

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I dont know how I am supposed to this problem without the size of the cup

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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.

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.5 gram and .05 cm^3

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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?

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1,000 joules

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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.

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100,000

100 million

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Compare the number of grains of sand with the number of stars in our galaxy, that number estimated to be about 100 billion.

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100 million:100 billion

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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.

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??

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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?

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.0001 kg/ m^3

@& It takes 100 cm to make a meter.

So it takes 100^3 cm^3 to make a meter^3.

That is, it take a million cm^3 to make a m^3.

So that would be a million grams per m^3.*@

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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?

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height from 100 meters

Gravity is 9.8 m/s

I tried to look up this problem along with the ones following and I was stumped when it gives you the diameter which means you can find the radius which also means you can find the volume, but im not sure how to get the speed from that information.

@& The ball's acceleration is 9.8 m/s^2 downward. You know initial velocity and displacement, so you can figure out how fast it's going when it reaches the floor.*@

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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?

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How much KE does it lose, per gram of its mass, during the compression?

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How much KE does it gain, per gram of its mass, as it decompresses?

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How much momentum does it have, per gram of its mass, just before it first reaches the floor?

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How much momentum does it have, per gram of its mass, just after it first leaves the floor on its way up?

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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?

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a= dv/dt

.5 m/s^2=20m/dt=

dt= 10 seconds

@& Right idea, but `dv = 10 m/s and `dt = `dv / a, not `dv * a.*@

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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?

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fnet=ma

1700kg(.5m/s^2)

fnet=850 kg m/s^2

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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?

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gravity= 9.8 m/s =V

dt= .32

1.4 meters

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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?

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@& Not a bad start. Check my notes, then try to revise at least the questions on which I inserted notes.

Take a few minutes to think through that last one also.*@