Newton's second law of motion gives us a measure of

$A$ jet engine works on the principle of Newton's:

What force would be needed to produce an acceleration of $4 \, m s^{-2}$ on a ball of mass $6 \, kg$?

$(a)$ State the law of conservation of momentum.
$(b)$ $A$ body of mass $2 \, kg$,initially moving with a velocity of $10 \, m s^{-1}$,collides with another body of mass $5 \, kg$ at rest. After the collision,the velocity of the first body becomes $1 \, m s^{-1}$. Find the velocity of the second body.

$A$ certain force exerted for $1.2 \, s$ raises the speed of an object from $1.8 \, m s^{-1}$ to $4.2 \, m s^{-1}$. Later, the same force is applied for $2 \, s$. How much does the speed change in $2 \, s$?

Explain the following:
$(i)$ Why do we jerk wet clothes before spreading them on a line?
$(ii)$ Why does dust fly off when a carpet is hit with a stick?
$(iii)$ Why do fruits fall off the branches in a strong wind?
$(iv)$ Why does a pillion rider fall forward when the driver of a two-wheeler suddenly applies brakes?