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.

$(a)$ Define momentum of a body.
$(b)$ $A$ ball is thrown vertically upward. What is its momentum at the highest point?
$(c)$ State the law of conservation of momentum.

$A$ bullet of mass $5\, g$ travelling at a speed of $120\, m s^{-1}$ penetrates deeply into a fixed target and is brought to rest in $0.01\, s$. Calculate
$(a)$ the distance of penetration in the target
$(b)$ the average force exerted on the bullet

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

$(a)$ State Newton's second law of motion. Use this law to find a method to measure force acting on an object.
$(b)$ From a rifle of mass $4 \ kg$,a bullet of mass $50 \ g$ is fired horizontally with an initial velocity of $40 \ m \ s^{-1}$. Calculate the initial recoil velocity of the rifle.

$A$ bullet of mass $5 \, g$ travelling at a speed of $120 \, m s^{-1}$ penetrates deeply into a fixed target and is brought to rest in $0.01 \, s$. Calculate: $(a)$ the distance of penetration in the target,$(b)$ the average force exerted on the bullet.