$A$ bullet of mass $10 \, g$ is fired with a velocity of $400 \, m s^{-1}$ from a gun of mass $4 \, kg$. What is the recoil velocity of the gun (in $, m s^{-1}$)?

What is momentum? Write its $SI$ unit. Interpret force in terms of momentum. Represent the following graphically:
$(a)$ Momentum versus velocity when mass is fixed.
$(b)$ Momentum versus mass when velocity is constant.

How would you arrive at a mathematical formula to measure force using the second law of motion?

Why is it advised to tie luggage kept on the roof of a bus?

Give reasons and state the laws related to these statements:
$(a)$ It is easier to push an empty box than to push a box full of books.
$(b)$ It is difficult for a fireman to hold a hose which ejects a large amount of water with high velocity.

$(a)$ How much momentum will an object of mass $10 \ kg$ transfer to the floor if it falls from a height of $0.8 \ m$? $(g = 10 \ m s^{-2})$
$(b)$ Explain why it is difficult for a fireman to hold a hose,which ejects a large amount of water at a high velocity.