$A$ ball of mass $0.1 \ kg$ undergoes a head-on collision with a stationary ball of unknown mass. If the $0.1 \ kg$ ball rebounds with $1/3$ of its original speed,the mass of the second ball is .......... $kg$.

$A$ sphere of mass $M$ moving with velocity $u$ undergoes a perfectly elastic head-on collision with another sphere of mass $m$ at rest. After the collision,their velocities are $V$ and $v$ respectively. Find the value of $v$.

$A$ body of mass $m$ having an initial velocity $v$,makes a head-on collision with a stationary body of mass $M$. After the collision,the body of mass $m$ comes to rest and only the body having mass $M$ moves. This will happen only when:

Two masses $m_A$ and $m_B$ moving with velocities $v_A$ and $v_B$ in opposite directions collide elastically. After the collision,the masses $m_A$ and $m_B$ move with velocities $v_B$ and $v_A$ respectively. The ratio $\frac{m_A}{m_B} = $

On a frictionless surface,a block of mass $M$ moving at speed $V$ collides elastically with another block of same mass $M$ which is initially at rest. After collision,the first block moves at an angle $\theta$ to its initial direction and has a speed $\frac{V}{3}$. The second block's speed after the collision is:

$A$ neutron travelling with a velocity $v$ and kinetic energy $E$ collides perfectly elastically head-on with the nucleus of an atom of mass number $A$ at rest. The fraction of total energy retained by the neutron is