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.

$A$ constant force of friction of $50 \ N$ is acting on a body of mass $200 \ kg$ moving initially with a speed of $15 \ m \ s^{-1}$. How long does the body take to stop? What distance will it cover before coming to rest?

Amar, Javed, and Rita were riding in a bus that was moving with a high velocity on a highway when a bug hit the windshield and its dead body got stuck on the windscreen. Amar and Javed began discussing the situation. Amar suggested that the change in momentum of the bug is much greater than that of the bus. After all, argued Amar, there was no noticeable change in the velocity of the bus compared to the obvious change in the velocity of the bug. Javed opined that since the bus was moving with a larger velocity, so it exerted a larger force on the bug, as a result of which it died. Rita disagreed entirely, arguing that both the bug and bus experienced the same force and a change in their momentum. Who do you agree with? Support your answer.

$(a)$ Define momentum. Write its $SI$ unit.
$(b)$ $A$ car and a truck have the same momentum. Whose velocity is more and why?
$(c)$ $A$ bullet of mass $20 \ g$ moving with a speed of $500 \ m s^{-1}$ strikes a wooden block of mass $1 \ kg$ and gets embedded in it. Find the speed with which the block moves along with the bullet.

The following is the distance-time table of an object in motion:

Time in seconds	Distance in metres
$0$	$0$
$1$	$1$
$2$	$8$
$3$	$27$
$4$	$64$
$5$	$125$
$6$	$216$
$7$	$343$

$(a)$ What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
$(b)$ What do you infer about the forces acting on the object?

State the law of conservation of momentum. Mention two factors which determine the momentum of a body. $A$ ball of mass $0.4 \ kg$ is thrown vertically upwards with a velocity of $10 \ m s^{-1}$. What will be its initial momentum and what would be its momentum at the highest point of its reach? If this change in momentum occurs in one second, find the negatively accelerating force acting on the ball, when it was going up.