Explanation : [tex]p_f=-p_i[/tex]
Momentum of a body is defined as the product of its mass and velocity.
i.e. [tex]p=m\times v[/tex]
So, when an object is moving, it has momentum.
If [tex]m_1[/tex] and [tex]m_2[/tex] are the masses of objects A and B and [tex]u_1\ and\ u_2[/tex] are their initial velocities. so, their initial momentum will be:
[tex]p_i=m_1u_1+m_2u_2[/tex]
If after collision it bounces back with same velocities, then final momentum becomes:
[tex]p_f=-m_1u_1+(-m_2u_2)[/tex]
-ve sign shows that the motion is in opposite direction.
so, [tex]p_f=-(m_1u_1+m_2u_2)[/tex]
or[tex]p_f=-p_i[/tex]
Hence, its final momentum is in opposite direction of initial momentum.
