question_answer 44)

Suppose a ball of mass m is thrown vertically upward with an initial speed v, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attain the speed v again before striking the ground. It implies that the magnitude of initial and final momentums of the ball are same. Yet, it is not an example of conservation of momentum. Explain why?

Answer:

  Momentum of a system remains conserved if no external force acts on the system. In the given example, there is gravitational force acting on the ball which is an external force, so it is not an example of conservation of momentum.