$A$ girl of mass $50 \, kg$ jumps out of a moving boat of mass $300 \, kg$ onto the bank with a horizontal velocity of $3 \, m s^{-1}$. With what velocity will the boat begin to move backwards (in $, m s^{-1}$)?

What type of force is acting in the cases given above?

$A$ 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?

Air is blown onto a sail attached to a boat from an electric fan placed on the boat. Will the boat start moving?

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.

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.