An inelastic ball is projected with velocity v0=gh , at an angle α  to the horizontal, towards a wall at a  distance d from the point of projection. After collision the ball returns to the point of projection. What is the coefficient of restitution between ball and wall ( α=450 )

Time taken to return to the point of projection after  impact  =dev0cosα Total time of flight =dv0cosα+dev0cosα=dghcosα[1+ee]There is no change in the vertical component of the velocity after impact, therefore total time offlight remains unchanged.T=2v0sinαg=2ghsinαgdghcosα(1+ee)=2ghsinαgOr  (1+ee)=hsin2αdOr e=d(hsin2α−d)