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

Explain the following:
$(i)$ Why is it dangerous to jump out of a moving vehicle? How can the danger be minimised?
$(ii)$ Why does a boatman push the water backward with the oars while rowing a boat?

Suppose a ball of mass $m$ is thrown vertically upward with an initial speed $v$. Its speed decreases continuously until it becomes zero. Thereafter,the ball begins to fall downward and attains the speed $v$ again before striking the ground. It implies that the magnitude of the initial and final momentum of the ball are the same. Yet,it is not an example of the conservation of momentum. Explain why?

Write the relation for the collision of two balls $A$ and $B$ and state the related law.

Prove that $1 \text{ N} = 10^{5} \text{ dynes}$.

There are three solids made up of aluminium,steel,and wood,of the same shape and same volume. Which of them would have the highest inertia?