A ball of mass m falls vertically to the ground from a height h1 and rebound to a height h2. The change in momentum of the ball on striking the ground is

When ball falls vertically downward from height h1 its velocity v→1=2gh1and its velocity after collision  v→2=2gh2Change in momentumΔP→=m(v→2−v→1)=m(2gh1+2gh2)(because v→1 and v→2 are opposite in direction)