Conservation of linear momentum:

Let us consider two masses \( m_1 \) and \( m_2 \) moving with velocities \( u_1 \) and \( u_2 \) respectively, collide in an inertia frame of reference. Let \( v_1 \) and \( v_2 \) be the velocities of the particles after collision respectively. When no external force acts on the particles then their total linear momentum is conserved.

Therefore, \( m_1u_1+m_2u_2=m_1v_1+m_2v_2 \)

This relation holds good for elastic collisions and inelastic collisions.