The action-reaction forces:

Find the ratio of momentum of the two bodies $A$ and $B$ of masses $m$ and $4m$ respectively,moving with the same velocity $v$.

$A$ 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?

$(a)$ State the law of conservation of momentum.
$(b)$ Mention two factors which determine the momentum of a body.
$(c)$ Prove the law of conservation of momentum with clear explanation,diagram and equation.

While dusting a carpet,we suddenly jerk or beat it with a stick because:

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