Basic Maths and Units and DimensionsHard

Question

A boy throws a ball with speed u in a well of depth 14 m as shown. On bounce with bottom of the well the speed of the ball gets halved. What should be the minimum value of u such the ball may be able to reach his hand again? Assume that his hands are at 1 m height from top of the well while throwing and catching.
         

Options

A.10m/s
B.30m/s
C.20m/s
D.40m/s

Solution

Ball hits ground with velocity v =
Ball bounces back with velocity
If ball just rises by 15m then by conservation of energy:
= mg(15) ⇒ = mg(15) ⇒ u = 30m/s

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