A ball is dropped from a height of 10 m. It strikes the ground and rebounds up to a height of 2.5 m. During the collision the percent loss in kinetic energy is :

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Question

A ball is dropped from a height of 10 m. It strikes the ground and rebounds up to a height of 2.5 m. During the collision the percent loss in kinetic energy is :

100%

25%

50%

75%

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If ball is dropped from
   Point A :

   Then loss in potential energy
   = gain in kinetic energy
   KE₁= mgh = 10 mg
   Now ball rebounds up to height = 2.5 m,
   So now loss in kinetic energy = gain in potenital energy = mgh¢ = 2.5 mg
∴ % loss in K.E. = $\frac{10 mg - 2 .5 mg}{10 mg}$ × 100 %
               = $\frac{7.5}{10} \times 100$ = 75%