A student does 25 J of work on the handle of a pencil sharpener. If the pencil sharpener does 20 J of work on the pencil, what is the efficiency of the sharpener?

80%

Explanation:

Efficiency of machine = work output/work input  ×100 %

From question, work output = 20J

Work input = 25J.

Therefore efficiency = 20/25 × 100 %

Efficiency = 20×4 %

Efficiency = 80%

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