Question

what is the efficiency of a lawn mower's engine when the heat input is 1,000 joules and the waste heat is 750 joules

Answer 1

The answer would be 25%
Hope that helps

Answer 2

Answer:

25%

Explanation:

Efficiency of an engine is calculated by dividing the energy output over the energy input and expressing that as a percentage.  

Efficiency = $\frac{energy output}{energy input}$ x 100%

Given,  

Heat input = 1000 J  

Heat wasted = 750 J

Heat used = 1000 J – 750 J = 250 J  

Efficiency = $\frac{250 J }{1000 J}$ x 100% = 25%