Use the worked example above to help you solve this problem. A W = 47.5 N (10.7

Question

Use the worked example above to help you solve this problem. A W = 47.5 N (10.7 lb) weight is held in a person's hand with the forearm horizontal, as shown in the figure. The biceps muscle is attached d = 0.03021 m from the joint, and the weight is l = 0.353 m from the joint. Find the upward force F exerted by the biceps on the forearm (the ulna) and the downward force R exerted by the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. F = N R = N 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 8.19 times 10^2 N. (a) Under these circumstances, what maximum weight would you attempt to lift? (b) What force would your biceps apply while lifting this weight? N

Explanation / Answer

a) Apply net torque about bisep = 0

R*d - (l-d)*W = 0

8.19*10^2*0.03021 - (0.353 - 0.03021)*w = 0

w = 8.19*10^2*0.03021/(0.353 - 0.03021)

= 76.7 N

b) now Apply, Fnety = 0

F_bisep - R - W = 0

F_bisep = W + R

= 76.7 + 8.19*10^2

= 895.7 N

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