Two bodies of masses $2\ kg$ and $4\ kg$ are moving with velocities $2\ m/s$ and $10\ m/s$ respectively along the same direction. The velocity of their centre of mass will be ......... $m/s$.

$A$ man of mass $M$ stands at one end of a plank of length $L$ which lies at rest on a frictionless surface. The man walks to the other end of the plank. If the mass of the plank is $3M$,the distance that the man moves relative to the ground is:

Two bodies of $6 \,kg$ and $4 \,kg$ masses have their velocities $5 \hat{i}-2 \hat{j}+10 \hat{k}$ and $10 \hat{i}-2 \hat{j}+5 \hat{k}$ respectively. Then the velocity of their centre of mass is

Show that the total momentum of a system of particles is equal to the product of the total mass of the system and the velocity of the centre of mass.

$A$ child sits stationary at one end of a long trolley moving uniformly with a speed $V$ on a smooth horizontal floor. If the child gets up and runs about on the trolley in any manner,what is the speed of the $CM$ of the (trolley + child) system?

Discuss the explosion of a projectile.