$A$ ball is thrown vertically downwards with velocity $\sqrt{2gh}$ from a height $h$. After colliding with the ground,it just reaches the starting point. The coefficient of restitution is:

Two identical balls $A$ and $B$ having velocities of $0.5 \, m s^{-1}$ and $-0.3 \, m s^{-1}$ respectively collide elastically in one dimension. The velocities of $B$ and $A$ after the collision respectively will be

$Assertion$ : 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.

In the figure,determine the type of collision. The masses of the blocks,and the velocities before and after the collision are given. The collision is

$A$ 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:

$A$ car of mass $400 \ kg$ is moving with a speed of $72 \ km/h$. It collides with a truck of mass $4000 \ kg$ moving in the same direction with a speed of $9 \ km/h$. After the collision,the car rebounds with a speed of $18 \ km/h$. Find the speed of the truck after the collision in $km/h$.