A standard bowling ball weighs 17 pounds.You wish to hold a bowling ball in fron

Question

A standard bowling ball weighs 17 pounds.You wish to hold a bowling ball in front of you, with the elbowbent at a right angle. Assume that your biceps attaches to yourforearm at 2.5 cm out from the elbow joint, and that your bicepsmuscle pulls vertically upward, that is, it acts at right angles tothe forearm. Also assume that the ball is held 38 cm out from theelbow joint. Let the mass of your forearm be 5.8 kg and assume its center of gravity is located 19cm out from the elbow joint. How much force must your biceps muscleapply to forearm in order to hold out the bowling ball at thedesired angle?

Explanation / Answer

1 lb (mass) = .454 kg 17 lb = 7.72 kg 7.72 * 9.8 * .38 + 5.8 * 9.8 * .19 = 39.5 N-m torque byweight of ball and forearm F * .025 = torque exerted by biceps F = 39.5 / .025 = 1582 N   (about 355 lbforce)

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