The coefficient of restitution $e$ for a perfectly elastic collision is

Ball $A$ moving at $12\  m/s$ collides elastically with $B$ as shown. If both balls have the same mass, what is the final velocity of ball $A$ ? ................$m/s$

A spring-block system is resting on a frictionless floor as shown in the figure. The spring constant is $2.0 N m ^{-1}$ and the mass of the block is $2.0 kg$. Ignore the mass of the spring. Initially the spring is in an unstretched condition. Another block of mass $1.0 kg$ moving with a speed of $2.0 m s ^{-1}$ collides elastically with the first block. The collision is such that the $2.0 kg$ block does not hit the wall. The distance, in metres, between the two blocks when the spring returns to its unstretched position for the first time after the collision is. . . . . .

$A$ ball is of mass $m$, strikes a smooth ground at angle $\alpha$ as shown in figure and is deflected at angle $\beta$. The coefficient of restitution will be

A truck moving on horizontal road towards east with velocity $20\, ms^{-1}$ collides elastically with a light ball moving with velocity $25\, ms^{-1}$ along west. The velocity of the ball just after collision

A heavy body moving with a velocity $30\, m/s$ and another small object at rest undergo  an elastic collision. The latter will move with a velocity of .............. $\mathrm{m}/ \mathrm{s}$