Physics 201 MWF10:20 Fall 1999 (Ford)

Exam IV Chapts. 12-15 in Cutnell and Johnson 4th ed.

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

(3 pts) 1. A circular hole is cut through a flat brass plate. When the temperature of the plate is increased the diameter of the hole

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


(4 pts) 2. At T = 400 K the translational rms speed of a molecule of an ideal gas is 500 m/s. The number of moles is kept constant and the temperature of the gas is increased to 800 K. At 800 K what is the rms speed of a molecule of the gas?

a)  500 m/s
b)  1000 m/s
c)  250 m/s
d)  707 m/s <---ANS
e)  354 m/s


(3pts) 3. An isolated system undergoes an irreversible process. The entropy of the system

a)  increases <---ANS
b)  decreases
c)  remains the same since entropy is conserved


(3 pts) 4. Consider process 1 ----> 2 shown in the sketch. If Q = 0 for this process then the internal energy change is

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


(3 pts) 5. Consider process 1 ----> 2 shown in the sketch. If heat flows out of the system during this process then the internal energy change is

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


(3 pts) 6. A monatomic ideal gas expands (volume increases) while the pressure is kept constant. During this process

a)  heat flows into the gas <---ANS
b)  heat flows out of the gas
c)  there is no heat flow


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) 7. A copper can is filled to the brim with 6.0 × 10^-4 m³ of a liquid when both the can and the liquid have a temperature of 15°C. When the can and liquid are heated to 60°C, 3.0 × 10^-6 m³ of liquid spills over. The coefficient of volume expansion of copper is 51 × 10^-6 (C°)^-1 What is the coefficient of volume expansion of the liquid?

Ans. ____1.62 × 10^-4 (C°)^-1_____


(16 pts) 8. 0.20 kg of ice at T = -20°C is added to a mass m of water at T = 60°C. If no heat is lost to the surroundings and the final temperature is 30°C, what is the mass m of the water that was originally there? Note: 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.___0.797 kg___


(16 pts) 9. A rod consists of a 0.60 m length of aluminum joined to a 0.50 m length of brass, as shown. The free end of the aluminum piece is maintained at 100°C and the free end of the brass piece is mantained at 0°C. The rod has uniform cross sectional area A. The loss of heat through the sides of the rod can be ignored. The thermal conductivity of aluminum is 240 J/(s·m·C°) and the themal conductivity of brass is 110 J/(s·m·C°). What is the temperature T of the point where the two metals are joined?

Ans. ____64.5 °C________________


(17 pts) 10. Two moles of a monatomic ideal gas goes through the cycle shown in the sketch. For the complete cycle the net heat flow is -800 J. Note: R = 8.31 J/mol·K.

a) Calculate the work done by the gas in the process A ----> B.

Ans. _____+1662 J____

b) What is the work done by the gas in the process C ----> A?

Ans.___-2462 J____


(16 pts) 11. A Carnot heat engine has an efficiency of 0.600 and the tempeature of its hot reservoir is 800 K.

a) Determine the temperature of its cold reservoir.

Ans. ___320 K____

b) If 3000 J of heat is rejected to the cold reservoir in one cycle, what is the work output of the engine during one cycle?

Ans. ____4500 J____