Biomechanics Problem Solution

You must make a reasonable assumption that the COG is mid-way along the arm at 25cm. You should have a mass of 10kg at the hand, a force of 30N at 25cm (the COG) and Freaction at the shoulder (pointing up) in your free body diagram.

Sum F=0

Freaction = 30N [up] +10kg*9.81N/kg [up]

Freaction = 30N +98.1 N [up]

Freaction = 128.1 N [up]

Sum M=0

Mreaction + (-30N)(25cm) + -98.1N (50cm) = 0

Mreaction = 750 N*cm +4905 N*cm

Mreaction = 5655 N*cm [counter clockwise]

Mreaction = 56.55 N*m [counter clockwise]