The large quadriceps muscle in the upper leg terminates at its lower end in a te

Question

The large quadriceps muscle in the upper leg terminates at its lower end in a tendon attached to the upper end of the tibia (Figure a). The forces on the lower leg when the leg is extended are modeled as in Figure b, where T with arrow is the force in the tendon, F with arrowg,leg is the gravitational force acting on the lower leg, and F with arrowg,foot is the gravitational force acting on the foot. Find T when the tendon is at an angle of = 25.0° with the tibia, assuming Fg,leg = 27.6 N, Fg,foot = 15.0 N, and the leg is extended at an angle = 40.0° with respect to the vertical. Also assume the center of gravity of the tibia is at its geometric center and the tendon attaches to the lower leg at a position one-fifth of the way down the leg. -----------N

Explanation / Answer

w=weight of leg =27.6 N

F= weight of foot = 15.0 N

Applying law of conservation of torque at point of

Tnet = 0

T*L/5*sin25 – w*L/2*sin40 = F*L*sin40 =

T/5*sin25- 27.6/2*sin40 -15*sin40 =0     => T = 219 N

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