Question

An engine does 15.0 kj of work while exhausting 37.0 kj to the cold reservoir. What is the efficiency of the engine?

Answer 1

Answer:

28.8 %

Explanation:

The efficiency of an engine is given by:

$\eta = \frac{W}{Q_{in}}$

where

W is the useful work done

$Q_in$ is the heat in input

For this machine, we have

W = 15.0 kJ is the work done

$37.0 kJ$ is the heat exchausted to the cold reservoir, so the total amount of heat in input is

$Q_{in} = 15.0 kJ + 37.0 kJ=52.0 kJ$

And so the efficiency is

$\eta=\frac{15.0 kJ}{52.0 kJ}=0.288$

which corresponds to 28.8 %.