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Homework Help: Arm problem, Static Equilibrium

  1. Dec 4, 2008 #1
    1. The problem statement, all variables and given/known data

    (a) Calculate the magnitude of the force, FM, required of the "deltoid" muscle to hold up the outstretched arm shown in the figure. The total mass of the arm is 3.3 kg.

    (b) Calculate the magnitude of the force FJ exerted by the shoulder joint on the upper arm
    2. Relevant equations

    3. The attempt at a solution
    I got part a:

    How do I figure out Fj for part b?
  2. jcsd
  3. Dec 5, 2008 #2


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    Homework Helper

    Consider the effect of the cosine component of the deltoid force back into the joint.
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