In the human arm, the forearm and hand pivot about the elbow joint. Consider a s

Question

In the human arm, the forearm and hand pivot about the elbow joint. Consider a simplified model of a forearm/hand with the following data. The forearm/hand is 33.0 cm long, weighs 15.0 N, and the center of gravity is 15.0 cm from the elbow. The biceps muscle attaches to the forearm 3.80 cm from the elbow and always exerts a force perpendicular to the forearm.

(a) First, the forearm is horizontal and the a 80.0 N weight is held in the hand (at the end of the simplified forearm/hand model). What is the magnitude of the force exerted by the biceps on the arm?
(b) In the conditions of part (a), what is the magnitude and direction of the force the elbow joint exerts on the forearm?
(c) Next, still holding the 80.0 N weight, the person raises the forearm so that it makes an angle of 53.0

Explanation / Answer

(a) 80*0.33 + 15*0.0.15=F*.038

F=753.95N

(b) No force is applied by elbow on the forearm

(c) 80*0.33*cos 53+ 15*0.15*cos53=F*0.038

F=453.74N

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