A ball of mass $m$ is thrown vertically upward with an initial speed Its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fell downward and attains the speed $v$ again before striking the ground. It implies that the magnitude of initial and final momentum of the ball are same. Yet, it is not example of conservation of momentum. Explain why?
(CBSE Sample Paper)
Momentum of the system is conserved only if no external force acts on the system. However, in the given example, gravitational force acts on the ball when it moves upward or when it falls downward. Therefore, it is not the example of conservation of momentum.
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