# Solved > 41) A heat engine operating at maximum efficiency:1875933 …

41) A heat engine operating at maximum efficiency has an efficiency of 35.0%. The temperature of the hot reservoir is 700 K. What is the temperature of the cold reservoir?

A) 200 K

B) 245 K

C) 350 K

D) 455 K

E) 600 K

42) A heat engine operating at maximum efficiency has an efficiency of 25%. The temperature of the cold reservoir is 300 K. What is the temperature of the hot reservoir?

A) 350 K

B) 375 K

C) 400 K

D) 450 K

E) 500 K

43) The ocean thermal energy conversion project uses the surface water near tropical islands with a temperature of 20.0°C as the hot temperature reservoir, and the water at some depth, with a temperature of 5.0°C, as the cold temperature reservoir for a heat engine. What is the maximum efficiency of an engine running between those two temperatures?

A) 4.7%

B) 5.1%

C) 7.9%

D) 15%

E) 30%

44) A certain Carnot engine has Th = Tc + 35K, and an efficiency of 20.0%. What is Th?

A) 70.0 K

B) 140 K

C) 175 K

D) 210 K

E) 245 K

45) A Carnot engine has an efficiency of 83.0% and performs 4500 J of work every cycle. How much energy is discharged to the lower temperature reservoir every cycle?

A) 922 J

B) 833 J

C) 744 J

D) 3735 J

E) 5422 J

46) A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the refrigerator in order to remove 250 J of heat from the interior?

A) 60 J

B) 120 J

C) 250 J

D) 480 J

E) 1050 J

47) An air conditioner with a coefficient of performance of 3.5 uses 30 kW of power. How much power is it discharging to the outdoors?

A) 30 kW

B) 75 kW

C) 105 kW

D) 135 kW

E) 210 kW

48) An ideal, reversible heat pump is taking heat from the outside air at -10.0°C and discharging it into the house at 18.0°C. What is the coefficient of performance of this heat pump?

A) 10.4

B) 9.44

C) 0.644

D) 0.533

E) 0.0962

49) A Carnot air conditioner operates between an indoor temperature of 20°C and an outdoor temperature of 39°C. How much energy does it need to remove 2000 J of heat from the interior of the house?

A) 105 J

B) 130 J

C) 780 J

D) 520 J

E) 340 J

50) The compressor in a certain Carnot refrigerator performs 480 J of work to remove 150 J of heat from the interior of the refrigerator. How much heat must the coils behind the refrigerator discharge into the kitchen?

A) 110 J

B) 150 J

C) 330 J

D) 480 J

E) 630 J

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