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

η=Q₁-Q₂ /Q₁
Q₂=800J
η=0.2
Q₂=Q₁ (1- η)
Q₁=Q₂/(1- η)=800/(1-0.2) =1000 J

W= Q₁-Q₂ =1000-800=200 J

Answer 2

Work = Energy output(Eo).

Eff. = Eo/(Eo+800) = 0.20
Eo = 0.2(Eo+800)
Eo = 0.2Eo + 160
0.8Eo = 160
Eo = = 200 J.