Body of mass M is much heavier than the other body of mass m. The heavier body with speed v collides with the lighter body which was at rest initially elastically. The speed of lighter body after collision is

Three bodies having masses $$5 \mathrm{~kg}, 4 \mathrm{~kg}$$ and $$2 \mathrm{~kg}$$ is moving at the speed of $$5 \mathrm{~m} / \mathrm{s}, 4 \mathrm{~m} / \mathrm{s}$$ and $$2 \mathrm{~m} / \mathrm{s}$$ respectively along $$X$$-axis. The magnitude of velocity of centre of mass is

Assertion Two particles moving in the same direction do not lose all their energy in completely inelastic collision.

Reason Principle of conservation of momentum holds true for all kinds of collisions.