If you stand on one foot while holding your other leg up behind you, your muscles apply a force to hold your leg in this raised position. We can model this situation as in (Figure 1). The leg pivots at the knee joint, and the force that holds the leg up is provided by a tendon attached to the lower leg as shown. Assume that the lower leg and the foot have a combined mass of 3.2kg and that their combined center of gravity is at the center of the lower leg.

 

a) How much force must the tendon exert to keep the leg in this position?

b) As you hold your leg in this position, the upper leg exerts a force on the lower leg at the knee joint. What is the magnitude of this force?

c) What is the direction of the force exerted by the upper leg on the lower leg at the knee joint?n

The tendon provides the torque to raise the lower leg. 5.0 cm- 50 cm