$A$ cricket ball of mass $70 \, g$,moving with a velocity of $0.5 \, m s^{-1}$ is stopped by a player in $0.5 \, s$. What is the force applied by the player to stop the ball (in $, N$)?

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?

In the following cases,identify the direction of the net force acting on the objects:
$(a)$ $A$ car drives around a circular race track at a constant speed.
$(b)$ Earth moving around the sun.
$(c)$ $A$ ball,rolling across a grassy field,slowly comes to a stop.

Give two examples in each case,of a force that:
$(i)$ lifts
$(ii)$ pushes
$(iii)$ pulls
$(iv)$ stretches
$(v)$ compresses
$(vi)$ resists
$(vii)$ attracts
$(viii)$ squeezes

Define momentum and state its $SI$ unit. State the principle of conservation of momentum.

$A$ car of mass $1000 \, kg$ moving with a velocity of $15 \, m/s$ collides with a tree and comes to rest in $5 \, s$. What will be the force exerted by the car on the tree?