Physics 201 MWF10:20 Fall 2003 (Ford)

Exam IV Chapts. 12-15 in Cutnell and Johnson 6th ed.

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

(4 pts) 1. A small circular hole is drilled through a brass plate. When the temperature of the metal plate is increased, the diameter of the hole

a) increases<---------
b) decreases
c) remains the same


(4 pts) 2. The temperature of an ideal gas is held constant while the pressure is increased. During this process the work W done by the gas is

(a) zero
(b) positive
(c) negative<---------


(4 pts) 3. In a reversible isothermal process (T = 0) for n moles on ideal gas the volume of the gas decreases. In this process the entropy of the gas

(a) increases
(b) decreases<---------
(c) stays the same


(4 pts) 4. A Carnot engine operates between reservoirs at 600 K and 300 K. In one cycle 800 J of heat energy is put into the engine from the hot reservoir. In one cycle, how much heat energy flows from the engine into the cold reservoir?

(a) zero
(b) 200 J
(c) 400 J<---------
(d) 800 J
(e) 1600 J
(f) 3200 J


(4 pts) 5. n moles of a monatomic ideal gas initially has internal energy 400 J, volume 0.20 m³ and pressure 800 Pa. The volume of the gas is then doubled, to 0.40 m³, and the pressure is halved, to 400 Pa. What is the internal energy of the gas after this process has occured?

(a) 100 J
(b) 200 J
(c) 400 J<---------
(d) 800 J
(e) 1600 J


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) 6. Ice with an initial temperature of -40 °C is added to 0.200 kg of water that has an initial temperature of 45 °C. The system is in a container of negligible mass. No heat is lost to the surroundings. If the final temperature of the system is 25 °C, what is the mass of the ice that was added to the water? (Note: For water L_f = 3.35 × 10⁵ J/kg, L_v = 22.6 × 10⁵ J/kg and c = 4186 J/(kg·C°). For ice, c = 2000 J/(kg·C°).

Ans. ____0.0322 kg_____


(18 pts) 7. Three moles of a monatomic ideal gas are taken from state A to state C along the path shown. Process A to B is at a constant volume of 0.30 m³ and process B to C is at a constant pressure of 500 Pa. The final volume at state C is 0.80 m³. States A and C have the same temperature. For the process A to B to C, what is the total heat flow and does heat flow into the gas or out of the gas?



Ans. Q = ___250 J_____

into or out of gas? ____into___


(16 pts) 8. Two moles of a monatomic ideal gas absorb 1600 J of heat energy and the gas expands and does 2600 J of work. If the initial temperature of the gas is 300 K, what is the temperature of the gas after this process has occurred?

Ans. _____260 K_____


(14 pts) 9. In one cycle a heat engine does 240 J of work and rejects 80 J of heat into the cold reservoir. What is the thermal efficiency of the engine?

Ans. ____75%_____


(16 pts) 10. Two rods, one of aluminum and the other of copper, are joined end to end. The cross-sectional area of each rod is 6.0 × 10^-4 m². The length of the aluminum rod is 0.300 m and the length of the copper rod is 0.200 m, so the composite rod has length 0.500 m. The free end of the aluminum rod is placed in boiling water (T = 100 °C) and the free end of the copper rod is placed in ice water (T = 0 °C). The sides of the rods are insulated, so no heat is lost to the surroundings. How much heat is conducted by the composite rod in 60 s? (Note: The thermal conductivity of aluminum is k = 240 J/(s·m·C°) and the thermal conductivity of copper is k = 390 J/(s·m·C°).



Ans. _____2042 J____