The Achilles tendon is attached to the rear of the foot as shown in (Figure 1) .

Question

The Achilles tendon is attached to the rear of the foot as shown in (Figure 1) . A person elevates himself just barely off the floor on the "ball of one foot." Assume the person has a mass of 85 kg and D is twice as long as d.

Part A

Find the tension FT in the Achilles tendon (pulling upward).

Express your answer to two significant figures and include the appropriate units.

Part B

Find the (downward) force FB exerted by the lower leg bone on the foot.

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

force balance in y-direction

Ft - Fb + N = 0 ..............(1)

N = mg (normal force)

torques balance about center of foot

d*Ft - D*N = 0

D = 2*d

Ft = 2*N

Ft = 2*m*g

Ft = 2*85*9.81 = 1667.7 N

in eq.1

Fb = Ft + N

Fb = 2mg + mg = 3*mg

Fb = 3*85*9.81 = 2501.55 N

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