4. (25 points) In the crouching position, the lower leg is held in equilibrium through the action of the patellar ligament, which is attached to the upper tibia and runs over the kneecap. As depicted in figure below, the forces acting on the lower leg are N, R, and T. If the lower leg is in equilibrium, determine the magnitude of the tension T in the patellar ligament, and the direction and magnitude of R. Assume that the tension acts at a point directly below the point of action of R. Take the normal force equal to 100 lb (half the body weight), the weight of the leg Wleg as 20 lb, and the angle a = 40° (for the leg at a 45° angle). Is the ACL in tension? Patellar ligament 1.5" T 7" leg ↑R 7" 7 Figure 3: Forces on the lower leg during crouching.

Fig: 1