Question

On a hot day, yon are in a sealed, insulated room. The room contains a refrigerator, operated by an electric motor. The motor does work at the rate of 438 W when it is running. The refrigerator removes heat from the food storage space at a rate of 450 W when the motor is running. In an effort to cool the room, you open the refrigerator door and let the motor run continuously. At what net rate is heat added to (+) or subtracted from (−) the room and all of its contents?

Answer 1

Answer: Heat is removed from the room at 12W

Explanation: Since the room is insulated, no heat can leave the room except it is air conditioned.

The engine does work at a rate ∆W/t = 450W

Power is generated at a rate ∆Q/t = 438W

Net change in energy = (∆Q-∆W)/t

= ∆Q/t - ∆W/t

= (438 - 450)W

= 12W