$A$ neutron moving with velocity $u$ collides elastically with an atom of mass number $A$. If the collision is head-on and the initial kinetic energy of the neutron is $E$, then the final kinetic energy of the neutron after the collision is:

$A$ smooth sphere $A$ of mass $m$ collides elastically with an identical sphere $B$ at rest. The velocity of $A$ before collision is $8 \ m/s$ in a direction making $60^{\circ}$ with the line of centers at the time of impact.
$(i)$ The sphere $A$ comes to rest after collision.
$(ii)$ The sphere $B$ will move with a speed of $8 \ m/s$ after collision.
$(iii)$ The directions of motion of $A$ and $B$ after collision are at right angles.
$(iv)$ The speed of $B$ after collision is $4 \ m/s$.
The correct option is:

Two billiard balls undergo a head-on collision. Ball $1$ is twice as heavy as ball $2$. Initially,ball $1$ moves with a speed $v$ towards ball $2$ which is at rest. Immediately after the collision,ball $1$ travels at a speed of $v/3$ in the same direction. What type of collision has occurred?

$A$ 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 $\,kg$)

The bob $A$ of a pendulum released from $30^o$ to the vertical hits another bob $B$ of the same mass at rest on a table as shown in Figure. How high does the bob $A$ rise after the collision? Neglect the size of the bobs and assume the collision to be elastic.

$A$ ball of mass $1 \ kg$ moving along the $X$-direction collides elastically with a stationary ball of mass $m$. The first ball (mass $= 1 \ kg$) recoils at a right angle to its original direction of motion. If the second ball starts moving at an angle $30^{\circ}$ with the $X$-axis,the value of $m$ must be (in $kg$)