If say, a object such as a ball with velocity v m/s and mass m kg collides with a stationary solid wall, and the ball rebounds back with a velocity of v' m/s while the wall remains stationary, is momentum conserved? Since the wall is stationary, I would assume that the initial and the final momenta of the wall are zero. Hence applying the law of conservation of momentum, p initial = p final mv=mv' But then the velocity of the ball is in the opposite direction after the impact, so how would I justify the conservation of momentum in this case? Also, would the collision be elastic? (assuming the wall does not deform) Thanks!