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CBSE Class 9 Answered

<div>a ball is dropped from a height of 10m. if the energy of the ball reduces by 40%after striking the ground,how much high can the ball bounce back. (g = 10)</div>
Asked by mansi | 28 Feb, 2015, 07:55: PM
Expert Answer
Given that the ball is dropped from a height, h1 = 10 m
Potential energy at h1 = mgh1
Given g =10 m/s2 , h1 = 10 m
Therefore the potential energy at h1 = m×10×10
 = 100m J
On striking the ground level, the ball looses 40% of its initial energy:
i.e. (40/100)× 100m J
=40m J
The energy left on striking the ground = 100 m J - 40 m J
= 60 m J
So the final energy of the ball , mgh2 = 60m J
i.e h2 = (60 /10) 
        = 6 m
Hence the ball will bounce back to a height of 6 m
Answered by Jyothi Nair | 01 Mar, 2015, 12:12: PM

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