100 m 300 PROBLEM 16.80 An athlete performs a leg extension on a machine using a 20 kg mass at A located 400 mm away from the knee joint center O. Biomechanical studies show that the patella tendon inserts at B, 100 mm below point O and 20 mm from the center line of the tibia (see figure). The mass of the lower leg and foot is 5 kg, the CG of this segment is 300 mm from the knee, and the radius of gyration about the knee is 350 mm. Knowing that the leg is moving at a constant angular velocity of 30 degrees per second when 0 = 60°, determine (a) the force F in the patella tendon, (b) the magnitude of the joint force at the knee joint center O.