A ball is projected from a given point with velocity u at some angle with the horizontal and after hitting a vertical wall returns to the same point. Show that the distance of the point from the wall must be less than `(eu^2)/((1+e)g)`, where e is the coefficient of restitution.

Explanation

`(x)/(ucosalpha)+(x)/(eucosalpha)=T=(2usinalpha)/(g)`
or `x=(eu^2sin2alpha)/((1+e)g)impliesx_(max)=(eu^2)/((1+e)g)`
at `2alpha=90^@`