$A$ ball of mass $2 \,kg$ collides with another ball of mass $M$ at rest. If the collision is elastic and after the collision, the first ball moves with $\frac{1}{3}$ of its initial velocity in the same direction, then the mass of the second ball is: (in $\,kg$)

Consider the following statements $A$ and $B$ and identify the correct answer:
$A$. In an elastic collision,if a body suffers a head-on collision with another of the same mass at rest,then the first body comes to rest while the other starts moving with the velocity of the first one.
$B$. Two bodies of equal mass suffering a head-on elastic collision merely exchange their velocities.

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

$A$ neutron makes a head-on elastic collision with a stationary deuteron. The fractional loss of energy of the neutron in this collision is:

$A$ light particle moving horizontally with a speed of $12\ m/s$ strikes a very heavy block moving in the same direction at $10\ m/s$. The collision is one-dimensional and elastic. After the collision,the particle will

$A$ block of mass $m$ moving on a frictionless surface at speed $v$ collides elastically with a block of the same mass,initially at rest. Now,the first block moves at an angle $\theta$ with its initial direction and has speed $v_1$. The speed of the second block after the collision is