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))`

Explanation

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