$A$ body of mass $m$ moving with a velocity $v$ collides head-on with another body of mass $2m$ at rest. If the coefficient of restitution between the two bodies is $e$,then the ratio of the velocities of the two bodies after collision is:

$A$ ball is dropped from a height of $10 \ m$ and hits the roof of an elevator moving downwards with a velocity of $1 \ m/s$. What is the rebound velocity of the ball in $m/s$?

$A$ ball of mass $2m$ and a system of two balls with equal masses $m$ connected by a massless spring are placed on a smooth horizontal surface (see figure). Initially, the ball of mass $2m$ moves with velocity $u_0$ along the line passing through the centres of all the balls and the spring, whereas the system of two balls is at rest. Assuming that the collision between the individual balls is perfectly elastic, the ratio of vibrational energy stored in the system of two connected balls to the initial kinetic energy of the ball of mass $2m$ is

$A$ body of mass $m$ moving with velocity $u_1$ collides elastically with another body of the same mass $m$ at rest. After the collision,they move at an angle of .............. $^o$ to each other.

$A$ perfectly rigid billiard ball of kinetic energy $E_k$ collides with an identical stationary ball. After the collision,the kinetic energy of the first ball becomes $E'_k$. Then,which of the following is true?

Two small particles of equal masses start moving in opposite directions from a point $A$ in a horizontal circular orbit. Their tangential velocities are $v$ and $2v$,respectively,as shown in the figure. Between collisions,the particles move with constant speeds. After making how many elastic collisions,other than that at $A$,will these two particles again reach the point $A$?