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Question
A ball is dropped from a height of 10 m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back? (g = 10 m s–2)
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Solution
Let the mass of the ball be m, then, the initial potential energy of the ball
= mgh = 10 x 10 x m
= 100 m J
Since the energy of the ball reduces by 40% after striking the ground, energy left with the ball = 60% of P.E.
= `60/100 xx 100 "m"`
= 60 m J
Let the ball bounce back to height W due to this remaining energy,
∴ mgh = 60 m
h = `(160"m")/"mg"`
= 6m
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