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 is the force in the tendon, F_g, leg is the gravitational force acting on the lower leg, and F_g, foot is the gravitational force acting on the foot. Find T when the tendon is at an angle of phi = 25.0 degree with the tibia, assuming F_g, leg = 36.6 N, F_g, foot = 14.5 N, and the leg is extended at an angle Theta = 40.0 degree 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.

Explanation / Answer

net torque is zero

torque about knee

Tsin250*L/5 - Fg.leg*L/2*sin400 - Fg,foot*L*sin400=0

Tsin250*1/5 - 36.6*1/2*sin400 - 14.5*1*sin400=0

T =249.4 N

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