I\'m working on physics homework and having trouble with thefollowing question..

Question

I'm working on physics homework and having trouble with thefollowing question...

A student (m = 63 kg) falls freelyfrom rest and strikes the ground. During the collision with theground, he comes to rest in a time of 0.0140 s. The average force exerted on him by the groundis +20000. N, where the upward direction is taken to be thepositive direction. From what height did the student fall? Assumethat the only force acting on him during the collision is that dueto the ground.

Any help would be much appreciated. Thanks!

Explanation / Answer

let the speed before hit the ground be v, after be 0
momentun P0 = mv, P1 = 0 impulse = F*t = 20000N*0.0140s = P =P1-P0=mv v = 20000N*0.0140s/63kg = 4.44 m/s let the h of falling be h, for energy conservation, mgh = (1/2)mv2 h = v2/2g = (4.44m/s)2/2*9.8m/s2 = 1.01m answer: 1.01m

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