Q18 of 46 Page 247

An object of mass 1 kg is dropped from a height of 20 m. It hits the ground and rebounds with the same speed. Find the change in momentum. (Take g = 10 m/s2)

According to the equations of motion,

V2 = u2 + 2as


where v is the final velocity


u is the initial velocity


a is the acceleration


s is the displacement


Here acceleration is acceleration due to gravity,g.


So v = √(u2 + 2gs)


= √(0 + 2×9.8×20)


= √196


= 14 m/s


Initial momentum = mv


Final momentum = -mv


Change in momentum = mv-(-mv) = 2mv = 2×1×14 = 28 kgms-1


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