Part A Calculate the impulse experienced when a 75 kg person lands on firm groun

Question

Part A Calculate the impulse experienced when a 75 kg person lands on firm ground after jumping from a height of 2.7 Express your answer using two significant figures. J-550 kg.m/s Correct Part B Estimate the average force exerted on the person's feet by the ground if the landing is stiff-legged. With stiff legs, assume the body moves 1.8 cm during impact [Hint: The average net force on her which is related to impulse, is the vector sum of gravity and the force exerted by the ground.] Express your answer using two significant figures. avg= 1.1x105 N Correct Part C Estimate the average force exerted on the person's fect by the ground if the landing is with bent legs. When the legs are bent, assume the body moves about 42 cm during impact. Express your answer using two significant figures. 4700 N

Explanation / Answer

C)

consider the motion from top at height of 2.7 m to just before hitting the ground

v = speed just before hitting

using conservation of energy

kinetic energy gained = potential energy lost

(0.5) m v2 = mgh  

v = sqrt(2 gh)

v = sqrt(2 (9.8) (2.7)) = 7.3 m/s

d = stopping distance = 42 cm = 0.42 m

Favg = average force = ?

using work - change in kinetic energy theorem

Favg d = - (0.5) m v2

Favg (0.42) = - (0.5) (75) (7.3)2

Favg = - 4.8 x 103 N

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