Consider an elastic collision of a particle of mass $m$ moving with velocity $u$ with another particle of the same mass $m$ at rest. After the collision, the particles move at angles $\theta_1$ and $\theta_2$ with respect to the initial direction of motion. What is the sum of the angles $\theta_1 + \theta_2$ in degrees?

$A$ moving body with mass $m_1$ strikes a stationary mass $m_2$. What should be the ratio $\frac{m_1}{m_2}$ so as to decrease the velocity of the first body by $1.5$ times after the collision?

$A$ ball is dropped from a height of $80 \ m$ on a surface which is at rest. Find the height attained by the ball after the $2^{nd}$ collision if the coefficient of restitution is $e = 0.5$.

$A$ molecule of mass $m$ moving with velocity $v$ makes $5$ elastic collisions with a wall of a container per second. The change in momentum of the wall per second in $5$ collisions will be:

The bob of a simple pendulum (mass $m$ and length $l$) is dropped from a horizontal position. It strikes a block of the same mass $m$ placed on a horizontal frictionless table. The collision is elastic. The kinetic energy of the block after the collision will be

$A$ ball of mass $m$ moving with speed $v$ collides elastically with an identical stationary ball which is initially at rest. After collision,the first ball moves at an angle $\theta$ to its initial direction and has speed $(v/3)$. The second ball moves in a straight line after the collision. Then,the speed of the second ball after the collision is: