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 P8.48. 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 4.0 kg, 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 are the magnitude and direction of this force?

The tendon provides the torque to raise the lower leg. 5.0 cm- FIGURE P8.48 50 cm