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Rotational dynamics/Rigid objects in equilibrium

  1. Dec 17, 2006 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations
    Net force of the Y vector: -F1 + F2 - weight = 0

    3. The attempt at a solution

    I tried to solve the equation thinking that m could = torque (torque=force X length of lever arm) but I couldn't figure out how to fit in that .025m spot in between the joint and the muscle. Not sure if the equation provided will really help. Any help is appreciated!
    Last edited: Dec 17, 2006
  2. jcsd
  3. Dec 17, 2006 #2


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    Science Advisor

    The question is tricky because the M force is drawn in the wrong direction. The M force is the blue arrow up, not a black arrow going right. Put an equation equal to 0 where clockwise moments are positive and counterclockwise are negative
    0 = (0.025)(M) + (0.15)(22) - (0.3)(111)
    M = 1200N

    That doesn't seem right. That's equivalent to 122kg, resting on 1 muscle.
  4. Dec 17, 2006 #3
    We have an answer sheet (it's a multiple choice question) and one of the answers is 1.2X10^3, and your equation makes sense, so...Thanks! I'm on some other forums (mostly car junk) and I've never gotten an answer that quick!
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