$(a)$ Name the force that keeps the object moving in a circular path with constant acceleration.
$(b)$ What would happen if this force is absent?

In oil tankers,some space is left at the top while filling them. Explain why.

$(a)$ State Newton's second law of motion and show that the first law of motion can be mathematically derived from the mathematical expression for the second law of motion.
$(b)$ A stone dropped from a window reaches the ground in $0.5 \, s$ (given $g = 10 \, m \, s^{-2}$):
$(i)$ Calculate the speed just before it hits the ground.
$(ii)$ What is the average speed during $0.5 \, s$?
$(iii)$ Calculate the height of the window from the ground.

State whether the following statement is true or false:
In any interaction,there are always at least two forces in play.

State the law of conservation of momentum. How does conservation of momentum take place in each of the following?
$(i)$ $A$ rocket taking off from ground.
$(ii)$ Flying of a jet aeroplane.

Which would require a greater force $-$ accelerating a $2 \ kg$ mass at $5 \ m s^{-2}$ or a $5 \ kg$ mass at $3 \ m s^{-2}$?