Question

What is the efficiency of an engine that does 288 J of work and exhausts 72 J of heat while taking in 360 J of heat?

A. 25%
B. 20%
C. 10%
D. 80%

Thanks!

Answer 1

If you're using the machine to heat your workshop, it's 20% efficient.

If you're using it to do work, it's 80% efficient.

Answer 2

Efficiency = 80 %

Step-by-step explanation:

It is given that,

Work done by the engine, W = 288 J

Heat exhausted by the engine, Q₂ = 72 J

Heat supplied to the engine, Q₁ = 360 J

Efficiency of the heat engine is defined as the ratio of output work to the supplied energy i.e.

`\eta=(W)/(Q_1)`

W = Q₁ - Q₂

So,
`\eta=1-(Q_2)/(Q_1)`

`\eta=1-(72)/(360)`

`\eta=0.8* 100`

`\eta=80\%`

Hence, the correct option is (D) i.e. efficiency = 80 %