$A$ ball is moving with velocity $4 \ m/s$ and collides head-on with another stationary ball of double the mass. If the coefficient of restitution is $0.2$,then their velocities (in $m/s$) after the collision will be:

$A$ smooth sphere moves on a horizontal surface with a velocity vector $2\hat{i} + 2\hat{j}$ before it strikes a vertical wall. The wall is parallel to the $\hat{j}$ vector,and the coefficient of restitution between the sphere and the wall is $e = 1/2$. What will be the velocity vector of the sphere after it strikes the wall?

$A$ large ball of mass $M$,moving with velocity $u$,strikes a small ball of mass $m$,which is at rest. After the collision,the small ball attains velocity $u$ and the large ball attains velocity $v$. What is the value of $v$?

$A$ ball moving with a velocity of $9 \ m/s$ collides with another similar stationary ball. After the collision,both balls move in directions making an angle of $30^{\circ}$ with the initial direction. After the collision,their speed will be $-$

$A$ body falling from a height of $10\,m$ rebounds from a hard floor. If it loses $20\%$ of its energy in the impact,then the coefficient of restitution is:

Two balls $A$ and $B$ having masses $1 \ kg$ and $2 \ kg$,moving with speeds $21 \ m/s$ and $4 \ m/s$ respectively in opposite directions,collide head-on. After the collision,$A$ moves with a speed of $1 \ m/s$ in the same direction. The coefficient of restitution is: