What is the effect of force when it is applied in the following cases?
$(a)$ $A$ balloon is pressed from opposite sides.
$(b)$ $A$ ball is hit with a bat.
$(c)$ $A$ spring is compressed.

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.

State whether the following statement is true or false:
Action and reaction act on the same body.

Two balls of the same size but of different materials,rubber and iron,are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so,in which direction? Will they move with the same speed? Give reasons for your answer.

What is the force required to accelerate a $2 \, kg$ mass by $5 \, m s^{-2}$ (in $, N$)?

It is required to increase the velocity of a scooter of mass $80 \ kg$ from $5 \ m s^{-1}$ to $25 \ m s^{-1}$ in $2 \ s$. Calculate the force required.