A ball after having fallen from rest under the influence of gravity for 6 s crashes through a horizontal glass plate, thereby losing two-third of its velocity. It then reaches the ground in 2 s, find the height of the plate above the ground.

Answer

`58.8`

Explanation

`v = u+at= 0 +g xx 6 " " :. V = 6g`
`s_(1)=1/2 g xx 36 = 2g`
When marble ball crashes through horizontal glass plate then velocity after crash is
`6g - 6g xx 2/3 = 2g`
Distance for remaining 2 seconds
` :. S_(2) = 2g xx 2 +1/2 g xx 4`
`= 4g +2g = 6g = 6 xx 9.8`
= 58.8 m .