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?

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

Answer:

Efficiency = 80 %      

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.

$\eta=\dfrac{W}{Q_1}$

W =  Q₁ - Q₂

So, $\eta=1-\dfrac{Q_2}{Q_1}$    

$\eta=1-\dfrac{72}{360}$    

$\eta=0.8\times 100$

$\eta=80\%$      

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