$A$ machine gun can fire $50 \, g$ bullets with a velocity of $150 \, m s^{-1}$. $A$ $60 \, kg$ stone is moving towards the machine gun with a velocity of $10 \, m s^{-1}$. How many bullets must be fired from the gun to just stop the stone in its tracks?

$A$ motorcar of mass $1200\, kg$ is moving along a straight line with a uniform velocity of $90\, km/h$. Its velocity is slowed down to $18\, km/h$ in $4\, s$ by an unbalanced external force. Calculate the acceleration and change in momentum. Also,calculate the magnitude of the force required.

In which direction do the following forces act when an object is in motion?
$(i)$ Frictional force
$(ii)$ Gravitational force
$(iii)$ Centripetal force

Two forces $F_{1} = 20 \, N$ and $F_{2} = 30 \, N$ are acting on an object in opposite directions as shown in the figure.
$(i)$ What is the net force acting on the object?
$(ii)$ What is the direction of the net force acting on the object?
$(iii)$ If the mass of the body is $10 \, kg$,what will be the acceleration produced in it?

State whether the following statement is true or false:
The force of friction is smaller in solids than in liquids.

Given below are some measuring units of different physical quantities:
$kg\, ms^{-2}, ms^{-2}, kg\, ms^{-1}, ms^{-1}, kg\, m^2 s^{-2}$
Select the units which measure force and momentum respectively.