The rate of change of momentum is

$A$ man weighing $60 \, kg$ runs along the rails with a velocity of $18 \, km \, h^{-1}$ and jumps into a car of mass $1 \, \text{quintal} \, (100 \, kg)$ standing on the rails. Calculate the velocity with which the car will start travelling along the rails.

If the time taken to bring a ball to rest from a certain velocity $v$ is reduced to half,what will be the changes in values of
$(a)$ Initial and final momentum.
$(b)$ Change of momentum.
$(c)$ Rate of change of momentum.

What is the momentum of an object of mass $m$, moving with a velocity $v$?

When a force of $40\, N$ is applied on a body,it moves with an acceleration of $5\, m s^{-2}$. Calculate the mass of the body. (in $kg$)

During a game of table tennis,if the ball hits a player,it does not hurt him. On the other hand,when a fast-moving cricket ball hits a spectator,it may hurt him. State the reason.