Physics 100 Energy in Today’s World Homework Ch. 4a
Prof. Menningen
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Name _________________________________
1.
What happens to essentially all the sound energy in a dorm room after it is generated by a
pair of stereo speakers?
a. It bounces around until it escapes out the window or door.
b. It is absorbed by your ears.
c. It is converted back to electrical energy by the speakers.
d. It heats up the room.
2.
What is the difference between heat and temperature?
a. Heat is the flow of thermal energy and temperature is the energy stored in
the motions and interactions of the molecules.
b. Heat is the energy stored in the motions and interactions of the molecules
and temperature is the flow of thermal energy.
c. Heat is the flow of thermal energy and temperature is a measure of the
average kinetic energy of the molecules.
d. Heat is a measure of the average kinetic energy of the molecules and temperature
is the flow of thermal energy.
3.
A cup of water and a swimming pool full of water are at the same temperature. Which of
the following statements about these two systems are correct?
a. The average molecular speed in the cup of water is less than that in the
swimming pool.
b. They contain the same amount of latent heat.
c. Their thermal energies are proportional to their masses.
d. They have the same thermal energies.
4.
In a container there are two kinds of gas, one with heavy molecules and one with very light
molecules.
(a) If both gases are at the same temperature, which gas molecules have the
greater average kinetic energy?
a. The light gas molecules.
b. The heavy gas molecules.
c. They have the same average kinetic energy.
(b) In this mixture of different gases, which molecules have the higher average speed?
a. The light gas molecules.
b. The heavy gas molecules.
c. They have the same average speed.
5.
Ice and air have the same specific heats. Would 100 calories of heat raise the temperature
of 1 liter of ice by the same amount as 1 liter of air? No – thermal energy Q is
proportional to mass, not volume… Q  mcT
6.
Why do climates near the coast tend to be more moderate than those in the middle of the
continent?
a. Because the coastal regions are at lower elevations.
b. Because thermal convection is suppressed near coastal regions.
c. Because water has a relatively high specific heat.
d. Because water has a relatively low thermal conductivity.
Physics 100 Energy in Today’s World Homework Ch. 4a
Prof. Menningen
p. 2 of 3
7.
Is it possible to increase the temperature of gas in a cylinder without any energy transfer as
heat? Explain.
The temperature of a gas is dependent upon its thermal energy. The first law of
thermodynamics states that there are two ways to change the thermal energy, and
therefore the temperature, of the gas: add heat or do work on the gas. Therefore,
compressing the gas with a piston will do work on the gas, transferring energy to the
gas, thereby increasing its thermal energy and hence its temperature. This can all be
accomplished without adding any heat.
8.
If a system has no change in thermal energy, we can say that
a. any heat gained by the system must have caused a decrease in temperature.
b. the system must not have done any work.
c. the system must not have lost or gained any heat.
d. any amount of work done by the system was equal and opposite to the heat gained.
9.
How much heat is required to raise the temperature of 800 g of water from 20.0°C to
35.0°C?
Q  mcT   800 g 1.00 cal/g  °C  35C  20C 
 12,000 cal  12 kcal  50.2 kJ
10. (a) How many joules of gravitational potential energy are converted to kinetic energy
when 305 grams of lead shot falls from a height of 60.0 cm?
1 kg
 0.305 kg
1000 g
1m
h  60.0 cm 
 0.600 m
100 cm
m  305 g 
E  mgh   0.305 kg  10 m/s 2   0.600 m   1.83 J
(b) How many calories of thermal energy are produced when the shot from part (a) lands if
none of the kinetic energy is converted to other forms?
TE  1.83 J 
1 cal
 0.437 cal
4.184 J
Physics 100 Energy in Today’s World Homework Ch. 4a
Prof. Menningen
p. 3 of 3
11. A typical jogger burns up food energy at the rate of about 40.0 kJ per minute. How much
time would it take to run off a piece of cake if it contains 400 (food) Calories?
Power 
t
E
t
E
400 Cal  4184 J/Cal  1 kJ/1000 J

 41.8 min  0.697 h
Power
40.0 kJ/min
12. When an ideal gas was compressed, its thermal energy increased by 220 J and it gave off
170 J of heat. How much work was done on the gas?
E  Won system  Qto system
W  E  Qto   220 J    170 J   390 J
13. If it takes 3350 cal to raise the temperature of a 500-g statue by 50ºC, what is the specific
heat of the material used to make the statue?
Q  mcT
Q
3350 cal
c

 0.134 cal/g/ C
mT  500 g  50C 