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Show your work Write your answer in the box when provided Staple the pages Use appropriate units Your leg(thigh + lower leg) has a mass of 12kg. The radius of gyration of the leg about the hip medical-lateral axis is 0.6 m when your knee is extended. You are about to swing your leg forward (hip flexion) to kick a ball. What is the moment of inertia of the leg about the hip joint? How much hip flexion torque is needed to flex your hip at an angular acceleration of 3 rad/s? Using Newton's 2^nd law (Sigma T = I alpha), describe 2 things that you can do to increase the acceleration of the leg (and velocity of the leg with is hits the ball) After you kick a ball, your leg angular rotation velocity decreased from 6 rad/s to 0rad/s over 0.3 seconds (follow through). Calculate the average hip extension torque that was produced during the follow through using the impulse-momentum relationship How does the average hip extension torque produced during the follow through change if the follow through lasted longer? Explain using the impulse-momentum relationship.

Explanation / Answer

a) moment of inertia, I = m k^2

where k = radius of gyration

I = 12 x 0.6^2 = 4.32 kg m^2

b) torque = I x alpha

     = 4.32 x 3 = 12.96 N m

c) Net torque = I x alpha

to increase the accelearation, increase the torque

Or decrease the moment of inertia

d) angular acc. = wf - wi / t = (0 - 6) / 0.3 = 20 rad/s

torque = I x alpha = 4.32 x 20 = 86.4 N m

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