Question

A student (m = 73 kg) falls freely from rest and strikes the ground. During the collision with the ground, he comes to rest in a time of 0.04 s. The average force exerted on him by the ground is +18000 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.

Answer 1

Answer:h=4.96 m

Explanation:

Given

mass of student m=73 kg

time to taken t=0.04  s

average Force $F_{avg}=18000 N$

Let h be the height from where student falls

and we know Impulse =change in momentum

$F\times time=m\times v$

velocity at bottom $=\sqrt{2gh}$

$v=\sqrt{2\times 9.8\times h}$

$18,000\times 0.04=73\times \sqrt{2\times 9.8\times h}$

$\sqrt{2\times 9.8\times h}=\frac{18,000\times 0.04}{73}$

$\sqrt{2\times 9.8\times h}=9.86$

$2\times 9.8\times h=97.279$

$h=4.96 m$