AP Physics  Equilibrium
posted by Henry on .
The Achilles tendon is attached to the rear of the foot as shown in the figure below. 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.
Here's the figure:
img687.imageshack.us/img687/663/img3552n.jpg
I have no idea where to start.

Well, sum moments about any point. I will do at the ball of the foot.
D*Fb(D+d)Ft=0
ft= D/(D+d) * Fb
But weight of the person is bearing down on the leg bone (assuming two legs, onehalf the weight). so Fb=72/2 g
Ft=2/3 72/2 g or about 235N 
1231N