Statement I : A rocket works on the principle of conservation of linear momentum.Statement II : Whenever there is a change in momentum of one body, the same change occurs in the momentum of the second body of the same system but in the opposite direction.

As the fuel in rocket undergoes combustion, the gases so produced leave the body of the rocket with large velocity and give upthrust to the rocket. If we assume that the fuel is burnt at a constant rate, then the rate of change of momentum of the rocket will be constant. As more and more fuel gas burnt, the mass of the rocket goes on decreasing and it leads to increase of the velocity of rocket more and more rapidly.