Question

A material has a heat capacity at constant volume C that is unchanging over a wide temperature
range. Two identical bodies made of this material, at initial temperature T and 9T, respectively, are
used to drive a heat engine. The maximum amount of work that can be obtained from this engine is

Answer 1

$$W=\eta Q=C(9T-T)\left(1-\frac{T}{9T}\right)=\frac{64}{9}CT$$