C). Suppose your mass is 61 kg and the height of the wall is 1.00 m. If you land

Question

C). Suppose your mass is 61 kg and the height of the wall is 1.00 m. If you land stiff-legged, the time it takes you to stop may be as short as 2 ms, while if you bend your knees, it might be as long as 0.1 s. Calculate the average net force (in newtons) that would act on you in those two cases. (D). The net force on you while you are stopping includes both the force of gravity and the force of the ground pushing up on you. Which of these plays a larger role if you are injured? To answer that, for each of the two cases in part (c), calculate the upward force the ground exerts on you (in newtons) and compare its magnitude to the force of gravity on you.

Explanation / Answer

force of gravity=m*g=61*9.81=598.41 N velocity before landing=sqrt(2gh)=4.43 m/s force due to ground=|m(dv/dt)|=|61*(0-4.43)/2ms|=135115 N[for stiff-legged] force due to ground=|m(dv/dt)|=|61*(0-4.43)/0.1s|=2702.3 N[for bent knee] F(avg) for stiff legged=135115-598.41=134516.59 N upward F(avg) for knee bent=2702.3-598.41=2103.89 N upward if you are injured force due to ground plays a larger role

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