Assertion : There is no loss in energy in elastic collision.

Reason : Linear momentum is conserved in elastic collision.

Assertion : Even though net external force on a body is zero, momentum need not to conserved.

Reason : The internal interaction between particles of a body cancels out momentum of each other.

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