A ball is dropped on a horizontal surface. The sound of 1st collision is heard after 2 sec. The second collision is heard again 2 sec after the 1st collision. After what time (from `2^(nd)` collision) will we hear the 3rd collision?

Answer

1 sec

Explanation

`h=(1)/(2)g t^(2),t=sqrt((2h)/(g))`
`O=lsqrt(2gl)" "t_(1)-(1)/(2)g t^(2)`
`t_(1)=2l(sqrt(2gh))/(g)=sqrt((8e^(2)h)/(g))=2lxx2" "rArrl=(1)/(2)`
`t_(2)=sqrt((8e^(4)h)/(g))=1xxt_(1)=1sec`