A person holds a 1.42-N baseball in his hand, a distance of 2L = 31.7 cm from th

Question

A person holds a 1.42-N baseball in his hand, a distance of 2L = 31.7 cm from the elbow joint, as shown in the figure. The biceps, attached at a distance of d = 2.38 cm from the elbow, exert an upward force of 12.1 N on the forearm. Consider the forearm and hand to be a uniform rod with a mas of 1.34 kg. (a) Calculate the magnitude of the net torque acting on the forearm and hand. Use the elbow joint as the axis of rotation. N middot m (b) If the net torque obtained in part (a) is nonzero, in which direction will the forearm and hi rotate?

Explanation / Answer

sigma T = Tbiceps - Tforearm - ball

= (12.1 * 0.0238) - (1.34 * 9.81 * 0.1585) - (1.42 * 0.317)

= 2.25 N.m

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clockwise motion [-ve net torque]

hand and forearm will rotate downward

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