Determine the combined moment about the elbow pivot (0) of the weights of the forearm and the sphere as shown in figure (1). Then find what must the biceps tension force be so that the overall moment about O become zero. (b=15) 55 (5+b) Ib 8 Ib 13"
Movement at the elbow is contributed by the weight of the spear and the weight of the fore arm.
b is given as 15
Then weight of the forearm= 5+15=20lb
Weight of the sphere =8lb
Horizontal distance between sphere and elbow =13 inches
Moment contributed by the sphere =8×13 lb.inches
Moment contributed by the sphere=104 lb.inches
Horizontal distance between center of mass of forearm and elbow = 6× cos (90°-55°) inches
Horizontal distance between center of mass of forearm and elbow = 6× cos (35°) inches
Horizontal distance between center of mass of forearm and elbow = 6× 0.81915 inches
Horizontal distance between center of mass of forearm and elbow = 4.915 inches
Moment contributed by the forearm= 20×4.915 lb.inches
Moment contributed by the forearm= 98.3 lb.inches
Total moment at elbow = 98.3+104= 202.3 lb.inches (total clockwise moment in downward direction)
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