A machine takes in 800 J of energy and gives out 160 J of useful work. What is its efficiency?
Answer and explanation
Correct answer: B. 20%
- Step 1: Efficiency = useful output ÷ input × 100. Step 2. 160 ÷ 800 × 100 = 20%. Answer: 20%. Why not the others: 80% is what you get if you give the wasted fraction. 640% is what you get if you give the wasted energy as a percentage. 40% is what you get if you round the answer up.
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