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A boy throws a ball of mass 20g vertically upwards .It rises to max. height of 100m. At what height will K.E. be reduced to 70%



Potential power of the ball at 100 m =  kinetic energy at the bottom
The Kinetic energy is = mgH = (20/1000) x 10 x 100 = 20 J.
From the law of convertion we can say 30 % the initial kinetic energy is converted into potential energy at that point as kinetic energy diereses to 70 % of the initial value.

So, assume the point at height as H

than , (30/100)*20=mgH (KE = 20)
         so, H=30m(ans)

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