Practice It: Use the worked example above to help you solve this problem. A W =

Question

Practice It:

Use the worked example above to help you solve this problem. A W = 53.5 N (12.0 lb) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.02921 m from the joint, and the weight is l = 0.340 m from the joint. Find the upward force vector F exerted by the biceps on the forearm (the ulna) and the downward force vector R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm.

F= 623

R= 570

Use the values from PRACTICE IT to help you work this exercise. Suppose you wanted to limit the force acting on your joint to a maximum value of 8.23 x 102 N.

(a) Under these circumstances, what maximum weight would you attempt to lift?

(b) What force would your biceps apply while lifting this weight?

Explanation / Answer

Moment of weight acting on joint = 53.5*0.340 = T N-m(say)

Moment of biceps force around joint = F*0.02921 N-m

So F = T/0.02921 = 623N

Diagram provided is not very clear with the problem.

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