PT245 HIP ABDUCTOR MUSCLE FORCE PROBLEM

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Solution Strategy

To find M, we must know the torque created by the hip abductor muscles. Since M is part of the torque, and since we know the angle of application of M (70 degrees), we can calculate the magnitude of M if we know the torque. This system is in a state of static equilibrium. That means nothing is moving (the person is balanced on the right lower extremity). Because the system is in static equilibrium, the torque created by body weight equals the torque created by the hip abductor muscles (otherwise the person would fall toward the side that was creating more torque). We can calculate the torque created by body weight because we know the perpendicular force (body weight) and the length of the moment arm (BC = 4"). Since the torque created by body weight equals the torque created by the hip abductor muscles, we can use that magnitude to solve for M.

     Solution Outline

• Find torque of body weight
• Body weight torque equals hip abductor muscle torque
• Use hip abductor muscle torque and length AB to find rotary component of M
• Use sine of angle BAM to find M

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