First slide
Collisions
Question

A rubber ball is dropped from a height of 5 m on a planet where the acceleration due to gravity is not known. On bouncing, it rises to 1.8 m. The ball loses its velocity on bouncing by a factor of

Moderate
Solution

If ball falls from height h1  and bounces back up to height h2  then  e=h2h1

Similarly if the velocity of ball before and after collision are v1 and v2 respectively then e=v2v1
So v2v1=h2h1=1.85=925=35
i.e. fractional loss in velocity=1v2v1=135=25

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