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Question
A ball of mass 50 g falls from a height of 2m and rebounds from the ground to 1.6 m. Find:
(i) The potential energy possessed by the ball when initially at rest.
(ii) The kinetic energy of the ball before it hits the ground.
(iii) The final potential energy of the ball.
(iv) The loss in kinetic energy of the ball on collision. (Take: g = 10N kg−1)
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Solution
Given : m = 50g = `50/1000`kg = 0.05 kg,
g = 10N kg−1,
h1 = 2m = 1.6 m.
(i) Initial potential energy possessed by the ball = mgh1
= 0.05 × 10 × 2 = 1.0 J.
(ii) The K.E. of the ball before it hits the ground
= Initial potential energy possessed by the ball
= 0.1 J
(iii) The final potential energy of the ball = mgh2
= 0.05 × 10 × 1.6
= 0.8 J.
(iv) The kinetic energy of the ball after striking the ground
= Final potential energy of the ball = 0.8 J
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