The quantitative definition of force is given by

The action-reaction forces:

$(a)$ Define inertia. There are three solid balls, made of aluminium, steel, and wood, of the same shape and volume. Which of them would have the highest inertia? Why?
$(b)$ Describe in brief an activity to illustrate the property of inertia of rest.

$A$ bullet of mass $5 \, g$ travelling at a speed of $120 \, m s^{-1}$ penetrates deeply into a fixed target and is brought to rest in $0.01 \, s$. Calculate: $(a)$ the distance of penetration in the target,$(b)$ the average force exerted on the bullet.

$A$ large truck and a mini bus both moving with a velocity of magnitude $V$ have a head-on collision and both of them come to a halt after that. If the collision lasts for $1 \, s$:
$(a)$ Which vehicle experiences the greater force of impact?
$(b)$ Which vehicle experiences the greater change in momentum?
$(c)$ Which vehicle experiences the greater acceleration?

$(a)$ $(i)$ Define momentum. State its $SI$ unit.
$(ii)$ An object of mass $50 \ kg$ is accelerated uniformly from a velocity of $4 \ m/s$ to $8 \ m/s$ in $8 \ s$. Find the magnitude of the force exerted on the object.
$(b)$ State Newton's first law of motion.