A 75-kg man stands on his toes by exerting an upward force through the Achilles tendon, as in Figure 9.42. (a) What is the force in the Achilles tendon if he stands on one foot? (b) Calculate the force at the pivot of the simplified lever system shown—that force is representative of forces in the ankle joint.
Step 1 of 4:
A man applies an upward force through Achilles tendon to stand on his toes. We are going to find the upward force applied to the Achilles tendon. The forces acting on the foot are represented in the free-body diagram. There are three forces acting on the system.
The mass of the man
The acceleration due to gravity
is the force acting through the Achilles tendon (upward)
is the force acting at the pivot (downward)
is the normal acting upward and equal to the weight in the opposite direction (upward)
Step 2 of 4:
The weight of the man is expressed as