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A man standing on the edge of a roof of a 20 m tall building projects a ball of mass 100 g vertically up with a speed of `10 ms^(-1)` and simultaneously throws another ball of same mass vertically down with the same speed. Find the kinetic energy of each ball when they reach the ground `(g = 10 ms^(-2))`.

Text Solution

Verified by Experts

Both the two balls reach the ground with the same velocity
`h=20m, m=100 g=10^(-1)kg, u=10 ms^(-1)`
`v^(2)-u^(2)=2gh`
`v^(2)=u^(2)+2gh=10^(2)+2xx10xx20-500`
K.E. of each ball `= (1)/(2)mv^(2)=(1)/(2)xx10^(-1)xx500=25 J`
`therefore` K.E. of ball = 25 J.
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