Physics 201 MWF10:20 Fall 2001 (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. Inside a copper block is a hollow spherical cavity of radius 5.0 cm. When the temperature of the block is increased does the radius of the cavity

a) increase?
b) decrease?
c) remain the same?


(3 pts) 2. A metal sphere is radiating heat energy at a rate of 60 W when it is at a Celsius temperature of 127 °C. If the temperature of the sphere is increased to 527 °C at what rate does it radiate energy?

a) 120 W
b) 249 W
c) 960 W
d) 4800 W
e) 17,790 W


(3 pts) 3. A system consisting of 5.0 mol of ideal gas expands and does 90 J of work on its surroundings. In this process the internal energy of the gas decreases by 30 J. The heat flow for this process is

a) 60 J into the gas
b) 60 J out of the gas
c) 120 J into the gas
d) 120 J out of the gas


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

a) increases
b) decreases
c) stays the same


(3 pts) 5. An ideal gas undergoes a reversible isothermal expansion (T = 0) in which the volume of the gas 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.

(15 pts) 6. A metal rod is 0.60 m long and has a cross sectional area of 0.0050 m². One end of the rod is maintained at 100 °C and the other is in contact with an ice-water mixture at 0 °C. It is found that the heat conducted by the rod causes 0.20 kg of ice to melt in 5.0 minutes. The ice-water mixture initially contains 5.0 kg of ice. Assume no heat is lost to the surroundings. Calculate the thermal conductivity of the metal. (Note: For water L_f = 3.35 × 10⁵ J/kg, L_v = 2.26 × 10⁶ J/kg and c = 4186 J/(kg·C°).)

Ans. ______________


(18 pts) 7. What mass m of ice at an initial temperature of -40 °C must be added to 0.40 kg of water at an initial temperature of 90 °C if the final temperature of the system is to be 10 °C? The applied pressure is 1 atm. (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. ______________


(14 pts) 8. Initially the translational rms speed of an atom of a monatomic ideal gas is 250 m/s. The pressure and volume of the gas are each doubled while the number of moles of the gas is kept constant. What is the final translational rms speed of the atoms?

Ans. _________________


(18 pts) 9. A Carnot heat engine operates using a hot reservoir at 700 K and a cold reservoir at 300 K. In one cycle the work output of the engine is 5000 J.

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

Ans. _________________

b) In one cycle, how much heat goes into the engine from the hot reservoir?

Ans. ______________

c) In one cycle, how much heat is rejected to the cold reservoir?

Ans. __________________


(20 pts) 10.

a) Five moles of an ideal monatomic gas with an initial temperature of 127 °C expands and in the process absorbs 1200 J of heat and does 2100 J of work. What is the final temperature of the gas?

Ans. _______________

b) In a constant pressure process the temperature of 5.0 moles of an ideal monatomic gas increases from 127 °C to 227 °C. What is the work done by the gas in the process?

Ans. ___________________

c) Five moles of an ideal monatomic gas undergoes a constant temperature process. In the process 800 J of heat flows into the gas.

Does the volume of the gas increase or decrease?

Ans. _______________

How much work is done by the gas in this process?

Ans. _______________

d) In a constant volume process for an ideal gas, 500 J of heat flows out of the gas. What is the change in internal energy of the gas?

Ans. ________________

Does the internal energy of the gas increase or decrease?

Ans.________________