When two identical masses,one of which is at rest,undergo an oblique elastic collision,what is the angle between the two bodies after the collision (in $^{\circ}$)?

$A$ neutron with velocity $v$ and kinetic energy $E$ collides head-on with a stationary nucleus of mass number $A$. What is the fraction of kinetic energy lost by the neutron?

$A$ smooth sphere $A$ is moving on a frictionless horizontal plane with an angular speed $\omega$ and its center of mass has a linear velocity $v$. It undergoes an elastic collision with an identical sphere $B$,which is initially at rest. After the collision,their angular speeds are $\omega_A$ and $\omega_B$ respectively. Neglecting friction,which of the following is true?

During an elastic collision between two bodies,which of the following statements are correct?
$I$. The initial kinetic energy is equal to the final kinetic energy of the system.
$II$. The linear momentum is conserved.
$III$. The kinetic energy during $\Delta t$ (the collision time) is not conserved.

$A$ uniform rod of mass $M$ and length $L$ is placed on a smooth horizontal surface. $A$ particle of mass $m$ moving with velocity $v$ strikes the rod at one end perpendicularly and comes to rest. The velocity of the centre of mass of the rod after the collision is:

$Assertion$ : If collision occurs between two elastic bodies,their kinetic energy decreases during the time of collision.
$Reason$ : During collision,intermolecular space decreases and hence elastic potential energy increases.