Question

A heat engine is 20% efficient. If it loses 800 J to the cooling system and exhaust during each cycle, the work done by the engine is:


200 J

1000 J

800 J

20 J

Answer 1

20% efficient means that out of the total work done, 20% is usable as a product. This is another way of saying 80% of work is lost.

This is algebra:
W * 0.80 = 800
W = 1000 J

So the total work done was 1000 J. 800 J was lost. The machine is 20% efficient.