The action-reaction forces:

What would be the force required to stop a car of mass $1000 \ kg$ and a loaded truck of mass $10000 \ kg$ in $2 \ s$,if they are moving with the same velocity of $5 \ m s^{-1}$?

$A$ man pushes a box of mass $50\, kg$ with a force of $80\, N$. What will be the acceleration of the box due to this force? What would be the acceleration if the mass were doubled?

The rate of change of momentum is

Calculate the ratio of momentum,when
$(i)$ velocity of an object is doubled.
$(ii)$ mass of an object is halved.
$(iii)$ both mass and velocity are increased by three times.

Give the magnitude and direction of the net force acting on:
$(a)$ a drop of rain falling down with a constant speed.
$(b)$ a cork of mass $10 \,g$ floating on water.
$(c)$ a kite skilfully held stationary in the sky.