A refrigerator has coefficient of performance 4.0. If its compressed does 50.0 J

Question

A refrigerator has coefficient of performance 4.0. If its compressed does 50.0 J of work during one cycle, how much heat does the refrigerator exhaust per cycle? 10. J 13 J 17 J 200 J 250 J To design a heat engine with an efficiency of 40% that exhausts heat to a reservoir of temperature 22 degree C, what minimum temperature must the hot reservoir have? 22 degree C 36.7 degree C 55.0 degree C 219 degree C 465 degree C Geochemists examining the granite in a mountain determine that the rode contains 70% as much 235U today as it did when the rock first formed. If the decay constant of 235U is r = 9.85 times 10^-10 year^-1, how old is this granite? 251 million years 305 million years 363 million years 711 million years 1, 020 million years

Explanation / Answer

7 )

COP = Q/W

4 = Q/50

Q = 200J

8 )

n = 1-Tc/Th

n = 40% = 0.4

Tc = 22oC = 295 K

Tc/Th = 0.6

Th = 295/0.6 = 491.67 K = 218.67 oC = 219 oC

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