A machine takes in 400 J of energy and gives out 100 J of useful work. What is its efficiency?
Answer and explanation
Correct answer: D. 25%
- Step 1: Efficiency = useful output ÷ input × 100. Step 2. 100 ÷ 400 × 100 = 25%. Answer: 25%. Why not the others: 75% is what you get if you give the wasted fraction. 300% is what you get if you give the wasted energy as a percentage. 45% is what you get if you round the answer up.
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