First Law of Thermodynamics Practice Problems
AP Physics
Name:
Period:
1. Is it possible for a system to lose energy even when heat is flowing into it? If not, why not? If so,
explain how such a thing is possible.
2. As a hot air balloon cools down it is compressed by the air around it. For this process, identify the
sign of the heat, the change in internal energy and the work.
3. As a popcorn kernel is warmed, the water inside the kernel vaporizes and then expands and does
work For this process, identify the sign of the heat, the change in internal energy and the work.
4. In an automobile engine, after unburned gas is injected into the cylinder, the piston compresses the
gas and raises its temperature. In the process, the walls of the cylinder get warmer as well. For this
process, identify the sign of the heat, the change in internal energy and the work.
5. Write definitions for each of the following term, sketch a P-V graph showing how a gas-filled piston
would perform such a process and explain what characteristic makes that type of process useful for
analysis:
Isobaric –
Isometric –
Isothermal –
Adiabatic –
6. When you pump a bicycle pump quickly, the compression is almost adiabatic because there isn’t
much time for the gas to exchange energy with anything. During a single pump, you do 36 J of work on
4.26 x 10-4 kg of air inside the cylinder.
a) How much does the internal energy of the air inside the pump change during a single pump?
b) Remember that internal energy simply depends on the specific heat at constant volume. How hot
will the air in the pump get after a single pump if it starts at room temperature?
7. On a sunny day, a 5 m3 tank full of 20 kg of helium heats up from 15 °C to 35 °C. How much heat
happens to the helium in the tank? [cv = 3115.8 J/(kg K) for helium]
8. A platter of birdseed is mounted on top of a gas-filled piston. As the birdseed on top of the platter is
eaten, the gas expands isothermally and does 4.17 J of work. How much heat occurs during this
process?
9. A child takes a long, partially inflated, cylindrical balloon, 4 cm in diameter and 50 cm long, into the
bathtub with them. As the balloon floats on the surface, the air in the balloon receives 34.9 J of energy
in the form of heat and expands isobarically until it is 58 cm long (and still the same width). How much
does the internal energy of the balloon increase? [Hint: what determines the pressure of the air inside
the balloon?]
10. When you place a room temperature (20 °C) soda bottle in the fridge, the 0.0022 kg of carbon
dioxide gas in the bottle cools isometrically by losing 23.5 J of energy as heat.
a) How much does the internal energy of the carbon dioxide gas change?
b) If the specific heat at constant volume is cV = 658 J/(kg K) for carbon dioxide, at what temperature
does the gas end up?
11. When you release 0.05 kg of air [cv = 785.7 J/(kg K)] from a compressed air tank, the high pressure
air expands adiabatically as it pushes outward on the low pressure air around it. In the process, the
temperature drops from 20 °C to 5 °C
a) How much does the internal energy of the air change as it cools down?
b) How much work does the compressed air do during the process?
12. You do 2 J of work to slowly and isothermally compress a single bubble on a sheet of bubble wrap.
How much heat takes place for the air inside that bubble?
13. 9.18 kg of neon gas in a freezer at –5 °C occupies 100 mL (0.0001 m3) of volume, halfway filling
the syringe that holds it. When the syringe is transferred to a 93 °C sauna, it expands isobarically until
grows to 136.2 mL. [Hint: what determines the pressure of the gas inside the syringe?]
a) How much work does the syringe do during the process?
b) How much does the gas’s internal energy change during the process? [cv = 620.5 J/(kg K) for neon]
c) How much heat happens during the process?