Two engines are identical except that engine A is two years old and engine B is new. If engine A does 15% less work than engine B under identical operating conditions, what is the ratio of the efficiencies of the two engines, e_A/e_B?

Question

Quizplus · Accepted Answer

Let the work done by engine B be W. Then the work done by engine A is 0.85W (since A does 15% less work than B). The efficiency of an engine is defined as the ratio of output work to input energy. Since the two engines are identical except for their age, we can assume that they have the same input energy. Therefore, the ratio of their efficiencies is equal to the ratio of their output work. That is, e_A/e_B = (0.85W)/W = 0.85.

Two Engines Are Identical Except That Engine a Is Two