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Unformatted text preview: direction to be positive. a) What is the force on the forearm from the triceps muscle? Since the block is in equilibrium, the tension in the string is equal to the gravitational force Mg on the block. Therefore, the force exerted at the persons hand is Mg and it is directed upward. We take counterclockwise as positive. The balance of torques equation around the contact point yields F t d 2 cos mgd 1 cos + Mgd 3 cos = 0 F t = (Mgd 3 mgd 1 )/d 2 = 2720 N, where m is the mass of the forearm. The force is directed upward. b) What is the force on the forearm from the humerus? We take our positive direction upward. The balance of forces equation yields Mg + F t F h mg = 0 F h = mg Mg F t = 2840 N The negative sign indicates it is directed downward....
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 Summer '08
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