# AP Physics 2 Free response Questions: Thermodynamics

### pV digrams

A proposed ocean power plant will utilize the temperature difference between surface seawater and seawater at a depth of 100 meters. Assume the surface temperature is 26° Celsius and the temperature at the 100-meter depth is 2° Celsius.

a) What is the ideal (Carnot) efficiency of the plant?

b) If the plant generates useful energy at the rate of 100 megawatts while operating with the efficiency found in part (a), at what rate is heat given off to the surroundings?

c) The diagram below represents the Carnot cycle for a simple reversible (Carnot) engine in which a fixed amount of gas, originally at pressure po and volume Vo follows the path ABCDA

In the chart below, for each part of the cycle indicate with +, -, or 0 whether the heat transferred Q and temperature change ΔT are positive, negative, or zero, respectively. (Q is positive when heat is added to the gas, and ΔT is positive when the temperature of the gas increases.)

 Q ΔT AB BC CD DA