a) A 30 kg kid jumps down from a treehouse and falls a distance of 1.80 m before

Question

a) A 30 kg kid jumps down from a treehouse and falls a distance of 1.80 m before she lands on the ground. What impulse must the ground exert on her when she lands?

b) If she lands stiff-legged and absorbs all of the impulse without bending her legs,what is the average force acting on her during the landing? Assume that her body moves only 1.0 cm downward from the instant of impact until she comes to rest.

c) Now if she decides to use her legs to absorb the impact, her body moves 35.0 cm downward after her feet initially hit the ground. What is the average force exerted on her now?

[Your answer here should tell you why it

Explanation / Answer

velocity at bottom = sqrt(2*g*h) = 5.9396 m/s

impulse = mv = 30*5.9396 = 178.19 Kg.m/s

b) F*d = 0.5*mv^2

F*0.01 = 0.5*30*5.9396^2

F = 5.29x10^4 N

c) F*0.35 = 0.5*mv^2 = 529.2

F = 1512 N

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