You are hurt when you kick a stone. Why?

$A$ 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.

An object experiences a net zero external unbalanced force. Is it possible for the object to be moving with a non-zero velocity? If yes,state the conditions that must be placed on the magnitude and direction of the velocity. If no,provide a reason.

State the reason for the following:
$(a)$ All cars are provided with seat belts.
$(b)$ It is dangerous to jump out of a moving bus.
$(c)$ Road accidents at high speeds are much worse than accidents at low speeds.

Write answers to the following:
$(i)$ Mention the direction in which the force of friction acts on a moving body. State its units.
$(ii)$ Name the property of bodies (or objects) to resist a change in their state of rest or of motion. Name the quantity that is a measure of this property.
$(iii)$ Name the physical quantity whose unit is $kg\, m s^{-1}$. Define this quantity.

$A$ large truck and a car,both moving with speed $v$,have a head-on collision and both of them come to a halt after that. If the collision lasts for $10 \ s$:
$(i)$ Which vehicle experiences the greater force of impact?
$(ii)$ Which vehicle experiences the greater momentum change?
$(iii)$ Which vehicle experiences the greater acceleration?
$(iv)$ Why is the car likely to suffer more damage than the truck?