Anouk does 150 J of work using a hammer to pull a nail out of a piece of wood, and the hammer does 105 J of work on the nail. What is the efficiency of the hammer?

Efficiency is useful work output divided by work input, multiplied by 100%. The hammer does 105 J of useful work on the nail from 150 J of input work, so its efficiency is (105 ÷ 150) × 100% = 70%. The correct choice is 70%.

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