(II) The Achilles tendon is attached to the rear of the foot as shown in Fig. 9-73. When a person elevates himself just barely off the floor on the "ball of one foot," estimate the tension FT in the Achilles tendon (pulling upward), and the (downward) force FB exerted by the lower leg bone on the foot. Assume the person has a mass of 72 kg and D is twice as long as d.
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FN ; the reaction force exerted from the ground to the ball of the foot at point A.
When the person starts to elevate from the ground all the weight of the body stays on the ball of the foot. So
FN: the downward force exerted by the bone at point B
FT : the force exerted by the tendon upward to lift the body at point T.