Assertion : Two particles are 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. [AIIMS 2018]

If two particles are initially moving in the same direction, then their resultant momentum will not be zero. Therefore,their resultant momentum cannot be zero after a completely inelastic collision.As, kinetic energy is directly proportional to the square of the momentum, hence kinetic energy cannot be zero. This implies, not all the energy in inelastic collision is lost.Hence, both Assertion and Reason are correct and Reason is the correct explanation of Assertion.