Leigh is doing a knee extension exercise using a 100 N weight
strapped to her ankle 40 cm from her knee joint. She holds her leg
so that the horizontal distance from her knee joint to the weight
is 30 cm.
1. What is the moment arm of the weight about the knee joint
axis?
2. For this position, what torque is created by the ankle
weight about her knee joint axis?
3. If the moment arm of the knee extensor muscles is 4 cm about
the knee joint axis, what amount of force must these muscles
produce to hold the leg in the position described? Consider that in
addition to the added weight at the ankle, the leg itself weighs
10kg, and the center of mass of the leg (shown by the crosshair
circle in the figure) is located at a distance of 10 cm from the
knee joint axis.