$A$ body is accelerated by applying a force of $30 \, N$. The change in the momentum of the body after $2 \, sec$ is ............ $kg \cdot m/s$.

$100$ balls,each of mass $m$,moving with speed $v$,simultaneously strike a wall normally and are reflected back with the same speed in time $t$. The total force exerted by the balls on the wall is

What is linear momentum? Write its $SI$ unit.

An engine pumps water continuously through a hose. Water leaves the hose with velocity $v$ and $m$ is the mass per unit length of the water jet. If this jet hits a surface and comes to rest instantaneously,the force on the surface is

Two trains $A$ and $B$ are running in the same direction on parallel rails such that $A$ is faster than $B$. Packets of equal weight are transferred between them. What will happen due to this?

$A$ $140\,g$ ball,in horizontal flight with a speed of $39.0\,m/s$,is struck by a bat. After leaving the bat,the ball travels in the opposite direction with a speed of $39.0\,m/s$. If the impact time $\Delta t$ for the ball-bat collision is $1.20\,ms$,calculate the average force in $N$ acting on the ball.