Chapter 15, Problem 30PE

(a) What is the hot reservoir temperature of a Carnot engine that has an eficiency of 42.0% and a cold reservoir temperature of $\text{21}0°\text{C}$ ? (b) What must the hot reservoir temperature be for a real heat engine that achieves 0.700 of the maximum eficiency, but still has an efficiency of 42.0% (and a cold reservoir at $\text{27}.0°\text{C}$ )? (c) Does your answer imply practical limits to the efficiency of car gasoline engines?