A body of mass $$5 \times 10^3 \mathrm{~kg}$$ moving with speed $$2 \mathrm{~m} / \mathrm{s}$$ collides with a body of mass $$15 \times 10^3 \mathrm{~kg}$$ inelastically and sticks to it. Then loss in $$\mathrm{KE}$$ of the system will be

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