You hang by your hands from a tree limb that is a height L = 3.8 m above the gro

Question

You hang by your hands from a tree limb that is a height L = 3.8 m above the ground, with your center of mass a height h = 2.8 m above the ground and your feet a height d = 1.8 m above the ground, as shown in the figure (not to scale). You then let yourself fall. You absorb the shock by bending your knees, ending up momentarily at rest in a crouched position with your center of mass a height b = 0.3 m above the ground. Your mass is M = 60 kg. You will need to draw labeled physics diagrams for the various stages in the process.

(b) What is your speed v at the instant when your feet first touch the ground? v = 7.245 Incorrect: Your answer is incorrect. m/s

(c) What is the magnitude F of the approximate average force exerted by the ground on your feet during the time when your knees are bending? (The force of the Earth is only Mg = 588 N; you notice the unusually big force on your feet.) F = N

Explanation / Answer

a.)

b.)

during free fall

V^2 = U^2 + 2aS

V ^2 = 0 + 2*9.81*1.8

V = 5.94 m/s

speed ( V) = 5.94m/s

b.)

So the kinetic energy = 1/2*m*v^2 = 1/2*56*5.9^2 = 1041J

Now The work done = K + U = 1041 + m*g*h = 1041 + 60*9.8*(1 - 0.3) = 1453.02 J

So F*d = 1453.02

so F = 1453.02/0.6 = 2075.74 N

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