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*11. A
student (m = 63 kg)
falls freely from rest and strikes the ground. During the collision with the
ground, he comes to rest in a time of
0.040 s. The average force exerted on him by the ground is +18 000 N,
where the upward direction is taken to be the positive direction. From what
height did the student fall? Assume that the only force acting on him during
the collision is that due to the ground. |
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Impulse-Momentum
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Since the ground brings the
student to rest. Since the made up
positive and we know is positive, we know that is down and must be negative, so - must be positive so we can drop the vector
signs. Solving for we get |
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Now consider conservation of
energy. We have no non-conservative
forces, so before the fall we have all gravitational potential energy and
just before they hit the ground we have all kinetic energy |
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Solve for h |
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