Two cars each of mass $1000 \ kg$ are moving in a straight line but in opposite directions. The velocity of each car is $5 \ m s^{-1}$ before the collision during which they stick together. What will be the velocity of the combined cars after collision (in $m s^{-1}$)?

If a body is in motion,is it necessary that it is being acted upon by a force?

Define momentum and state its $SI$ unit. State the principle of conservation of momentum.

$(a)$ Define momentum and mention its $SI$ unit.
$(b)$ From the velocity-time graph shown in the figure for a body of mass $5\, kg$,find the force on the body from:
$(i)$ $O$ to $A$ and $(ii)$ $B$ to $C$.
$(c)$ Which would require a greater force: accelerating a $2\, kg$ mass at $5\, m s^{-2}$ or a $4\, kg$ mass at $2\, m s^{-2}$?

What is the force required to accelerate a $2 \, kg$ mass by $5 \, m s^{-2}$ (in $, N$)?

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