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Gravtiational PE

A bread gives...

Question

A bread gives a boy of mass 40kg an energy of 21kJ. If the efficiency is 28%, then the height that can be climbed by him using this energy, is:

A

22.5m

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B

15m

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C

10m

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D

5m

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Solution

The correct option is B 15m
Efficiency $η = \frac{E_{0}}{E_{1}} \frac{28}{100} = \frac{m g h}{21 \times 1000} 2 \times 21 \times 10 = 40 \times 10 \times 4 h = 14.7 = 15 m$

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