Physics 201 MWF10:20 Fall 2002 (Ford)

Exam IV Chapts. 12-15 in Cutnell and Johnson 5th ed.

Multiple Choice questions. Circle the correct answer. No work needs to be shown.

(3 pts) 1. A circular hole is drilled in a steel plate. When the steel plate is heated so its temperature rises, the diameter of the hole

a) increases
b) decreases
c) remains the same


(4 pts) 2. An ideal gas undergoes an adiabatic expansion (Q = 0) in which the volume of the gas increases. In this process the internal energy of the gas

a) increases
b) decreases
c) stays the same
(4 pts) 3. An ideal gas undergoes a reversible isothermal process (T = 0) in which the number of moles remains constant and the pressure increases. In this process the entropy of the gas

a) increases
b) decreases
c) stays the same


On the following five problems show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(16 pts) 4. Initially, the internal energy of a sample of a monatomic ideal gas is 800 J. While the volume and number of moles are kept constant, the pressure is doubled.

a) After the pressure is doubled, what is the internal energy of the gas?

Ans._______________

b) What was the heat flow Q in this process? Did heat flow into or out of the gas?

Ans. Q = __________________

into or out of gas? ________________


(15 pts) 5. A metal rod has a uniform cross sectional area of 0.0050 m². The rod consists of a 0.4 m long section that is brass joined to a section of length L that is copper. The free end of the brass section of the rod is maintained at 100 °C and the free end of the copper section is in contact with an ice-water mixture at 0 °C. The temperature at the junction between the two parts of the rod is 70 °C. Assume no heat is lost to the surroundings and that steady state has been reached. The thermal conductivity of brass is k = 110J/(s·m·C°) and the thermal conductivity of copper is k = 390 J/(s·m·C°). (Note: For water L_f = 3.35 × 10⁵ J/kg, L_v = 2.26 × 10⁶ J/kg and c = 4186 J/(kg·C°).)



a) What is the length L of the copper section?

Ans. __________________

b) What mass of ice is melted in 2.0 minutes by the heat conducted by the rod?

Ans. ________________


(18 pts) 6. 0.20 kg of ice at an initial temperature of -20 °C is placed in thermal contact with a hot, solid piece of metal that has an initial temperature of 350 °C and a mass of 1.2 kg. The final temperature of the system is 70 °C. The applied pressure is 1 atm. If no heat is lost to the surroundings, what is the specific heat capacity of the metal? (For ice c = 2000 J/(kg·C°) and for water c = 4186 J/(kg·C°). For water L_f = 3.35 × 10⁵ J/kg and L_v = 2.26 × 10⁶ J/kg.)

Ans. _________________


(15 pts) 7. A Carnot heat engine operates between hot and cold heat reservoirs. In one cycle the engine receives 8000 J of heat energy from the hot reservoir and rejects 2000 J of heat energy into the cold reservoir.

a) How much work does the engine do in one cycle?

Ans.___________________

b) What is the thermal efficiency of this heat engine?

Ans. _________________

c) If the Celsius temperature of the hot reservoir is 350 °C, what is the Celsius temperature of the cold reservoir?

Ans. ___________________


(20 pts) 8. A monatomic ideal gas goes from state A to state C along the path shown in the sketch. Process A to B is at constant pressure and process B to C is at constant volume. The pressure for states A and B is 5.0 × 10⁵ Pa, the volume of state A is 0.30 m³, and the volume of states B and C is 0.50 m³. States A and C have the same temperature. The number of moles of gas is constant.



a) What is the pressure in state C?

Ans. ____________________

b) What is the total work done by the gas when it goes from state A to state C along the path shown?

Ans. ___________________

c) What is the total heat flow Q when the gas goes from state A to state C along the path shown? Does heat flow into the gas or out of the gas?

Ans. Q = __________________

into or out of gas? __________________