Two balls in free space are colliding with each other. Which of the following statement regarding linear momentum conservation of the system is true ?

In an elastic collision of two billiard balls which of the following quantities is not conserved during the short time of collision

In the figure shown, a small ball hits obliquely a smooth and horizontal surface with speed $u$ whose $x$ and $y$ components are indicated. If the coefficient of restitution is $\frac{1}{2}$, then its $x$ and $y$ components $v_x$ and $v_y$ just after collision are respectively

In $a$ one-dimensional collision, $a$ particle of mass $2m$ collides with $a$ particle of mass $m$ at rest. If the particles stick together after the collision, what fraction of the initial kinetic energy is lost in the collision?

Two small balls are fixed at the ends of a light rigid rod of length $0.4\  m$.The system is released from height $h = 5\  m$ with rod horizontal. The balls collide with the horizontal surface and rebound . The coefficient of restitution between $A$ and ground is $0. 6$ and that between $B$ and ground is $0.4$ . Find angular speed (in $rad/s$) just after the collision. Taking acceleration of free fall $10\ m/s^2$

Consider elastic collision of a particle of mass $m $ moving with a velocity $u$ with another particle of the same mass at rest. After the collision the projectile and the struck particle move in directions making angles ${\theta _1}$and ${\theta _2}$respectively with the initial direction of motion. The sum of the angles. ${\theta _1} + {\theta _2},$ is......$^o$