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.

A body of mass $$4 \mathrm{~kg}$$ moving with velocity $$12 \mathrm{~m} / \mathrm{s}$$ collides with another body of mass $$6 \mathrm{~kg}$$ at rest. If two bodies stick together after collision, then the loss of kinetic energy of system is