Question

3. A person is wearing a weight boot (150 N) and doing exercises to strengthen the knee extensor muscles. The center of mass of the weight boot is 0.35 meters from the center of rotation of the knee. The person's foot + shank has a weight of 40 N and its center of mass is 0.2 meters from the center of rotation of the knee. These distances are along the length of the shank.

1. When the shank is perpendicular to the ground, what is the total torque about the knee? (Be sure to use a free-body diagram.)

b. When the shank is held at a position where it is 20° below the horizontal (foot is lower than knee), what is the torque about the knee? (Be sure to use a free-body diagram. Note that the moment arm of the weight boot about the knee changes with knee angle.)

3. If the quadriceps muscle group has a moment arm of 0.025 m, what is the muscle force needed to hold the shank at 20° below the horizontal?

Answer 1