A person with m = 70 kg falls from a height of 1 m. How much is the force he exp

Question

A person with m = 70 kg falls from a height of 1 m. How much is the force he experiences from the ground as he stops if (a) he relies on the 1 cm thick soles of his shoes or (b) he bends his knees to allow for an extra 40 cm of stopping distance? If the tensile strength of the tibia is 8.3 times 10^7 Pa, and its compressive strength is 1.8 times 10^7 Pa, what the maximum height that a person can fall from in scenario (b) without breaking his legs? What assumptions do you need to make to answer this question?

Explanation / Answer

By conservation of energy

0.5*m*v2 = mgh

V2 = 2*9.8*1

v = 4.27 m/s

now question a

distance to stop = 1 cm

by equation of motion

V2 = 2as

a = 19.6/(2*0.01)

= 980 m/s2

force = m*a = 70*980 = 68600N

for part b

V2 = 2as

a = 19.6/(2*0.40)

= 24.5 m/s2

Force = 70*24.5 = 1715N

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