Physics 201 MWF10:20 Fall 1993 (Ford)
Exam IV Chapts. 14--20 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.
(14 pts) 1. A glass flask is filled up to a reference mark on the long stem
of the flask with 500 cm3 of liquid, with both the liquid and the
flask at a temperature of 60.0 °C. The coefficient of volume expansion
of the glass is 4.00×10-5/(C°). When the
flask and
liquid are cooled to 20.0 °C the level of liquid in the stem falls
8.0 cm. The cross-sectional area of the stem is 0.040 cm2; the change
of the area with temperature can be neglected. What is the coefficient of
volume expansion of the liquid?
Ans. ___5.6×10-5/(C°)___________
(18 pts) 2. A solid 0.80 kg sample of metal at a temperature of 600 °C is
placed in an insulated container of negligible mass and that holds a
mixture of 0.20 kg of water and 0.05 kg of ice. The ice-water mixture is
initially at a temperature of 0 °C. The final temperature of the
system is observed to be 30 °C. Assuming no heat is lost from the
system, what is the specific heat capacity c of the metal sample?
Ans. ___105 J/kg·C°___________
(16 pts) 3. One end of an insulated copper rod is maintained at
300 °C and the other end is placed in contact with water
that has a temperature
of 100 °C. The rod has a length of 50.0 cm and a cross-sectional area of
0.800 cm2. In a 10.0 minute time period the heat conducted by
the rod changes 5.0×10-3 kg of water into steam.
a) What is the heat current H in the rod?
Ans. ___18.8 J/s___
b) What is the thermal conductivity k of the metal rod?
Ans. ___588 J/m·s·C°___
(18 pts) 4. A Carnot engine whose high-temperature reservoir is at 500 K
takes in 600 J of heat at this temperature in each cycle and gives
up 320 J to the low-temperature reservoir.
a) What is the temperature of the low-temperature reservoir?
Ans. ___267 K___
b) What is the thermal efficiency of the cycle?
Ans. ___46.6 %___
c) How much mechanical work does the engine perform during each cycle?
Ans. ___+280 J___
(18 pts) 5. The volume of five moles of ideal gas is decreased from
0.08 m3 to 0.03 m3 while the pressure is kept
constant at 2.0×105 Pa.
For this gas Cv = 12.5 J/mol·K.
Calculate Q, W, and 
U
for this process. In each case be sure to
indicate whether the result is positive or negative.
Ans. Q = ___-2.50×104 J___
W = ___-1.00×104 J___
U = ___-1.50×104 J___
(16 pts) 6. When a system is taken from state a to state b
as shown in the
figure along the path acb, 90.0 J of heat flow into the system, and
60.0 J of work are done by the system.
a) How much heat flows into the system along path adb if the work done
by the system along this path is 20.0 J?
Ans. ___+50 J___
b) When the system is returned from b to a along the curved
path, the magnitude of the work done by the system is 45.0 J. Does the
system absorb or liberate heat, and how much? (That is, what is the sign
and magnitude of Q for this path?)
Ans. ___-75 J (liberates heat)___