Problem 2 In the picture below, the elbow joint acts like a hinge on the forearm

Question

Problem 2 In the picture below, the elbow joint acts like a hinge on the forearm. The bicep muscle exerts a vertical (upward) force, which pulls from a point 4.0cm from the hinge. The dumbbell in the hand exerts a vertical (downward) force (force of weight) 35 cm from the hinge. a) If the dumbbell has a mass of 10kg, how much torque does it exert on the forearm? b) How much force (magnitude) must the bicep exert on the forearm to keep the system in static equilibrium? You may neglect the mass of the forearm itself. Lifting muscle (biceps) Tendon Elbow joint 4.0 cm 35 cm Solution Part (a) =-34 N m Part (b) I Fbioepl = 858 N

Explanation / Answer

(A) torque = r x F = 0.35 x 10 x 9.81 clockwise

torque = 34.3 N m clockwise

or - 34.4 N m

(B) balancing torque about joint,

- 34.4 + (0.04 F) = 0

F = 858.4 N

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