Physics 201 MWF10:20 Fall 1996 (Ford)
Exam IV Chapts. 14--19 in SZY College Physics
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
Note: For water, c = 4190 J/kg·C;
Lv = 2256×103 J/kg;
LF = 333×103 J/kg
For ice, c = 2010 J/kg·C.
R = 8.314 J/mol·K;
1 atm = 1.01×105 Pa
(16 pts) 1. A glass flask is filled up to a reference mark on the long stem
of the flask with 200.0 cm3 of liquid, with both the liquid and the
flask at a temperature of 15.0 °C. The coefficient of volume expansion
of the liquid is 3.00×10-5 (C°)-1. When
the flask and
liquid are heated to 75.0 °C the level of liquid in the stem rises
4.0 cm. The cross-section area of the stem is 0.060 cm2; the change
of this area with temperature can be neglected. What is the coefficient of
volume expansion of the glass?
Ans. __________________
(16 pts) 2. An insulated copper rod is 0.30 m long and has cross-sectional
area 4.0×10-4 m2. The thermal conductivity of
copper is
k = 385 J/s· m· (C°).
One end of the rod is maintained at a
constant temperature of 400 °C by an oven. The other end of the
rod is in contact with 0.050 kg of ice that is at an initial temperature
of 0.0 °C. The ice is in an insulated container of negligible mass.
How much time does it take for the heat conducted by the rod to convert
the ice to water at a temperature of 0.0 °C?
Ans. _______________________
(18 pts) 3.
a) A Carnot heat engine has a thermal efficiency of 60%. The low-temperature
reservoir has a temperature of 180 K and in each cycle the engine performs
500 J of work. In each cycle how much heat does the engine give up to the
low-temperature reservoir?
Ans. _______________________
b) A Carnot refrigerator operates between a low-temperature reservoir at
a temperature of 180 K and a high-temperature reservoir at 300 K. In each
cycle the refrigerator takes in 600 J of heat energy from the low-temperature
reservoir. How much work is required to operate the refrigerator for one cycle?
Ans. ______________________
(22 pts) 4. A heat engine takes 3.0 moles of an ideal gas around the cycle
shown in the sketch. Process 1 to 2 is at constant pressure,
process 2 to 3 is adiabatic, and process 3 to 1 is at
constant volume. The temperature of the gas in states 1, 2, and 3 is
T1 = 300 K, T2 = 455 K, and
T3 = 600 K.
In the adiabatic process 2 to 3 the work is -9048 J.
a) For one cycle, what is the total work W? (You must say whether
W is positive or negative.)
Ans. ____________________
b) For one cycle, what is the total heat flow Q? (You must
say whether Q is positive or negative.)
Ans. ___________________
(24 pts) 5.
a) Five moles (n = 5.0 mol) of an ideal gas undergo an adiabatic
compression (Q = 0). The initial pressure and volume of the gas are
p1 = 4.0 atm and
V1 = 6.0×10-2 m3.
The final pressure and
volume are p2 = 7.1 atm and
V2 = 4.0×10-2 m3. For this gas
Cp = 29.2 J/mol· K. For this process calculate
(i) 
U Ans. __________________
(i) W Ans. _____________________
In each case you must say whether the answer is positive or negative.
b) Five moles (n = 5.0 mol) of an ideal gas undergo an isothermal
compression (T = 0).
The initial pressure and volume of the gas are
p1 = 4.0 atm and
V1 = 6.0×10-2 m3.
The final pressure and
volume are p2 = 6.0 atm and
V2 = 4.0×10-2 m3. For this gas
Cp = 29.2 J/mol·K. During this compression,
9830 J of heat energy flows out of the gas. What is the work
done by the gas? (You must say whether W is positive or
negative.)
Ans. _________________
c) In a constant pressure process, the volume of 5.0 moles of an ideal gas is
decreased from 6.0×10-2 m3 to
4.0×10-2 m3. The
constant pressure is 4.0 atm.
For this gas Cp=29.2 J/mol· K. For this process
calculate the change in internal energy U
for the gas.
(You must say whether U
is positive or negative.)
Ans. ___________________