assuming the lower leg and foot together have a combined mass of 4kg and the center of mass is located at the center of the lowerleg. the distance between the knee and tendon is 5 cm. the distancebetween the knee and foot is 50 cm. how much force must the tendonexert to keep the leg in this position. what is the magnitude of the force of the bone on the upper leg on the bone of the lowerleg.