Physics 201 MWF10:20 Fall 2004 (Ford)
Exam IV Chapts. 12-15 in Cutnell and Johnson 6th ed.
Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.
(12 pts) 1. A metal cup is completely filled with 600 cm3 of water at 20 °C. The cup and water are both heated to 90 °C and it found that 6.7 cm3 of the hot water spills over the edge of the cup. The coefficient of volume expansion for the water is 207 × 10-6 (C°)-1. What is the coefficient of volume expansion for the metal?
Ans. ______________________
(16 pts) 2. A metal rod is constructed by joining a rod of brass end-to-end with a rod of aluminum. Each piece of the rod has cross section 4.0 × 10-4 m2. The brass section has length 0.60 m and the aluminum section has length 0.40 m. The free end of the brass section is placed in boiling water (100 °C) and the free end of the aluminum section is in an ice-water mixture (0 °C). The thermal conductivity of brass is k = 110 J/(s·m·C°) and for aluminum it is k = 240 J/(s·m·C°).
a) What is the temperature T at the junction where the brass and aluminum sections are joined?
Ans. _______________
b) How many kg of ice changes phase (solid ----->liquid) each minute because of the heat conducted by the rod? (Note: For water Lf = 3.35 × 105 J/kg, Lv = 2.26 × 106 J/kg, and c = 4186 J/(kg·C°))
Ans. _____________________
(16 pts) 3. A Carnot heat engine operates between heat reservoirs at 327 °C and 127 °C. In one cycle the engine performs 800 J of work.
a) How much heat energy flows into the engine from the high temperature reservoir in one cycle?
Ans. ________________
b) How much heat energy is rejected by the engine into the low temperature reservoir in one cycle?
Ans. ___________________
(16 pts) 4.
a) Initially, the translational rms speed of the atoms of a monatomic ideal gas is 360 m/s. The pressure of the gas is tripled (P2 = 3P1) while the volume and number of molecules are kept constant. What is the rms speed of the atoms after the pressure has been increased?
Ans. _________________
b) A monatomic ideal gas at T =300 °C undergoes a reversible process in which the temperature is kept constant and the gas expands and does 400 J of work.
What is the entropy change of the gas?
Ans. ____________________
Does the entropy of the gas increase, decrease or stay the same?
Ans. ____________________
(8 pts) 5. The temperature of 5.0 moles of monatomic ideal gas increases from 323 °C to 403 °C while the pressure is kept constant. How much work is done by the gas during this process?
Ans. _______________________
(8 pts) 6. The temperature of 5.0 moles of monatomic ideal gas is kept constant at 300 K while the volume of the gas decreases. The magnitude of the work done by the gas during the process is |W| = 6000 J. What is the heat flow Q for this process and does heat flow into the gas or out of the gas?
Ans. Q = _____________________
into or out of the gas ________________
(8 pts) 7. In an adiabatic process (Q = 0) for 5.0 moles of monatomic ideal gas, the gas expands and does 6000 J of work. What is the change in the temperature of the gas? Does the temperature increase or decrease?
Ans. _____________________
increase or decrease? _________________
(8 pts) 8. 5.0 moles of a monatomic ideal gas undergo a process in which both the pressure and volume of the gas change. In the process the temperature of the gas decreases from 500 K to 420 K and the gas expands and does 1200 J of work. What is the heat flow Q for this process? Does heat flow into the gas or out of the gas?
Ans. Q = ______________________
into or out of the gas_______________
(8 pts) 9. 5.0 moles of monatomic ideal gas undergo a process in which the volume has the constant value 6.0 × 10-4 m3 and the pressure decreases from 3.0 × 105 Pa to 1.0 × 105 Pa. What is the change in internal energy of the gas?
Ans. _______________