What is the efficiency of an engine that does 80 J of work and exhausts 320 J of heat while taking in 400 J of heat?

The efficiency of an engine is calculated using the formula:

[ \text{Efficiency} = \frac{\text{Work Output}}{\text{Heat Input}} \times 100 ]

In this case, the work output is 80 J and the heat input is 400 J. Thus, the efficiency is:

[ \text{Efficiency} = \frac{80 , \text{J}}{400 , \text{J}} \times 100 = 20% ]

So, the efficiency of the engine is 20%.