What happens when two identical bodies moving in opposite directions undergo a perfectly elastic collision?

$A$ heavy steel ball of mass greater than $1\, kg$ moving with a speed of $2\, m/s$ collides head-on with a stationary ping-pong ball of mass less than $0.1\, g$. The collision is elastic. After the collision,the ping-pong ball moves approximately with a speed of ......... $m/s$.

$A$ block $A$ of mass $M$ moving with speed $u$ collides elastically with block $B$ of mass $m$ which is connected to block $C$ of mass $m$ with a spring. When the compression in the spring is maximum,the velocity of block $C$ with respect to block $A$ is (neglect friction):

$A$ particle of mass $m$ collides with another stationary particle of mass $M$. The particle $m$ stops just after the collision. The coefficient of restitution is:

In a carrom-board game,the striker and the coins are identical and of mass $m$. In a particular hit,the coin is hit when it is placed close to the edge of the board as shown in the figure,such that the coin travels parallel to the edge after the collision. If the striker is moving with speed $v$ before the strike,then the net impulse on the striker during the collision,if it moves perpendicular to the edge after the collision,is (assume all collisions to be perfectly elastic):

$A$ body of mass $1\,kg$ collides head-on elastically with a stationary body of mass $3\,kg$. After the collision,the smaller body reverses its direction of motion and moves with a speed of $2\,m/s$. The initial speed of the smaller body before the collision is $..........\,m/s$.