When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is
a. cm ln(T2/T1)
b. cm (T2/T1)
c. cm (T2 T1)/T1
d. cm (T2 T1)/T2
e. cm (T2 T1)/(T2 + T1)
[Ques. 2] Exactly 500 grams of ice are melted at a temperature of 32F. (Lice = 333 J/g.) The change in entropy (in J/K) is
a. 321
b. 146
c. 512
d. 610
e. 5 230
[Ques. 3] A vessel containing 5.0 kg of water at 10C is put into a refrigerator. The 1/7 HP motor (1 HP = 746 W) runs for 5.0 minutes to cool the liquid to the refrigerator's low temperature, 0C. What is the of the refrigerator?
a. 5.7
b. 4.6
c. 6.5
d. 7.2
e. 3.6
[Ques. 4] An engine is designed to obtain energy from the temperature gradient of the ocean. What is the thermodynamic efficiency of such an engine if the temperature of the surface of the water is 59F (15C) and the temperature well below the surface is 41F (5C)?
a. 3.5
b. 67
c. 31
d. 17
e. 96
[Ques. 5] An automobile engine operates with an overall efficiency of 12. How much energy is delivered as waste heat (in gallons of gasoline) for each 10 gallons of fuel burned?
a. 1.2
b. 8.8
c. 6.5
d. 4.7
e. 7.5
[Ques. 6] One kilogram of chilled water (0C) is placed in a freezer which is kept at 0F (18C). Approximately how much electric energy (in kilocalories) is needed just to freeze the water if the room temperature is maintained at 75F (24C)? (Lice = 333 J/g; cice = 209 J/g/C.)
a. 11
b. 15
c. 16
d. 13
e. 33
[Ques. 7] One kilogram of chilled water at 32F (0C) is placed in a freezer which is kept at 0F (18C). Approximately how much electric energy (in kilocalories) is needed to operate the compressor to cool this water to 0F if the room temperature is maintained at 75F (24C)? (Lice = 3.33 105 J/kg; cice = 2.09 103 J/kg/C)
a. 13
b. 1.5
c. 15
d. 16
e. 33
[Ques. 8] A homeowner has a new oil furnace which has an efficiency of 60. For every 100 barrels of oil needed to heat his house, how much (in barrels of oil) goes up the chimney as waste heat?
a. 20
b. 60
c. 40
d. 80
e. 10
[Ques. 9] An 800-MW electric power plant has an efficiency of 30. It loses its waste heat in large cooling towers. Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?
a. 1 200
b. 1 900
c. 800
d. 560
e. 240
[Ques. 10] A new electric power plant has an efficiency of 42. For every 100 barrels of oil needed to run the turbine, how many are essentially lost as waste heat (in barrels of oil) to the environment?
a. 21
b. 42
c. 58
d. 10
e. 79
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