A 63 kg woman is hopping up and down using only her ankles. During the propulsiv

Question

A 63 kg woman is hopping up and down using only her ankles. During the propulsive phase of the hop she generates an average power of 942.33 W over 180 ms while raising her center of mass 12 centimeters. Answer the following questions using the principles of work, energy & power.

a.What was the average work done on the woman by the ground reaction force during the propulsive phase?

b.What was the average ground reaction force experience by the woman during the propulsive phase?

c.What was the woman’s kinetic energy at takeoff?

d. How high was the woman’s hop? Use the Law of Conservation of Energy

Explanation / Answer

(a) average work done = Work done by power generated by her + work done by gravity

W = (942.33 x 0.180) + (-63 x 9.8 x 0.12)

W = 95.5 J

(C) W = F.d

F = 95.5 / 0.12 = 796 N

(D) from energy conservation,

KE = work done = 95.5 J  

(E) KE = m g h

95.5 = 63 x 9.8 x h

h = 0.155 m Or 15.5 cm

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