Please show all formulas used! A movie stunt requires that a 70 kg person jump o

Question

Please show all formulas used!

A movie stunt requires that a 70 kg person jump off a 30 m tall building and remain in freefall for the full 30 m.
The stunt directors devise a method of slowing the person down to a stop using a spring loaded platform at the
end of the 30 m. The spring constant for the platform is set to be 1000 N/m (we'll ignore the mass of the
platform I know, not good, but it will do for now.) How far down does the platform drop in catching the stuntperson?
If the maximum force that the body can handle without internal injuries is 10 times force of gravity, is
this platform adequate? Explain.

Points to the most clear and detailed.

Explanation / Answer

v = sqrt(2*g*h) = 24.24 m/s(before touching the plotform)



KE = 0.5*m*v^2 = 20580 J (before touching the plotform)

05*k*x^2 = 20580 (when the person comes to rest)

x = 6.4 m


Force exerted by plotform F = k*x = 1000*6.4 = 6400 N

F = 6400N

a = 6400/70 = 91.42 m/s^2

it is less than 10*9.8 m/s^2

so, it is adequate.

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