$A$ body falls from a height of $10 \ m$ onto the ground and rebounds to a height of $2.5 \ m$. The percentage loss in kinetic energy is ......... $\%$.

$A$ sphere collides with another sphere of identical mass. After collision,the two spheres move. The collision is inelastic. Then the angle between the directions of the two spheres is

$A$ ball $P$ moving with a speed of $v \ ms^{-1}$ collides directly with another identical ball $Q$ moving with a speed $10 \ ms^{-1}$ in the opposite direction. $P$ comes to rest after the collision. If the coefficient of restitution is $0.6$,the value of $v$ is (in $ms^{-1}$)

$A$ ball is dropped from a height of $20\,m$. If the coefficient of restitution for the collision between ball and floor is $0.5$,after hitting the floor,the ball rebounds to a height of $.............m$.

The sphere $A$ of mass $m$ moving with a constant velocity hits another sphere $B$ of mass $2m$ at rest. If the coefficient of restitution is $0.4$,the ratio of the velocities of the spheres $A$ and $B$ after collision is

$A$ sphere of mass $m$ moving with velocity $v$ collides head-on with another sphere of the same mass which is at rest. The ratio of the final velocity of the second sphere to the initial velocity of the first sphere is (where $e$ is the coefficient of restitution and the collision is inelastic).