A large metal ball is at rest, and a small rubber ball is moving at a high velocity. When they collide, the momentum of the small ball decreses. What happens to the momentum of the large metal ball?
According to the law of conservation of momentum, the total momentum of the system (both the large metal ball and the small rubber ball) must remain constant before and after the collision.
When the small rubber ball collides with the large metal ball and its momentum decreases, the momentum of the large metal ball must increase in order to maintain the total momentum of the system. Therefore, the momentum of the large metal ball increases as the momentum of the small rubber ball decreases.