During is colision between a closed system of particle in the absence of exerted force

Distinguish between a closed system and an open system.

Show that the total linear momentum of a system of particles is conserved in the absence of any external force. Also show that total linear momentum of the system is equal to the product of the total mass of the system and the velocity of its centre of mass.

In a system of particles, internal forces can change:

Internal forces acting in a system of particle can change

Internal forces acting in a system of particle can change

If net force on a system of particles is zero, then match the following.

During an elastic collision between two bodies, both of the exert forces on each other. These forces are