When a force of $40\, N$ is applied on a body,it moves with an acceleration of $5\, m s^{-2}$. Calculate the mass of the body. (in $kg$)

Which would require a greater force $-$ accelerating a $1\, kg$ mass at $10\, m s^{-2}$ or a $2\, kg$ mass at $4\, m s^{-2}$?

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.

Quick sand consists of very smooth and tiny grains of sand. What would happen if a man or a heavy animal steps over a patch of such sand in a desert?

$A$ player catching a moving ball moves his hand backwards. Why?

Explain the following:
$(i)$ Why is it difficult to walk on marshy land?
$(ii)$ Why does an air-filled balloon rise up slightly when punctured from below?
$(iii)$ Why does a swimmer push water backward with his hands in order to swim in the forward direction?