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प्रश्न
How fast should a boy weighting 30 kg run so that his kinetic energy is 375 joule?
उत्तर
We know that , K.E = `1/2` mv2
375 = `1/2` x 30 x v2
or v2 = `(375 xx 2)/30` = 25 m/s
or v = 5 m/s
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