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Problem with pulleys

  1. Sep 13, 2010 #1
    1. The problem statement, all variables and given/known data
    A patient's leg is held in position by 2 weights tht are connected through cables. The weight of the leg is W = 300N. L is the horizontal distance between the points where the cables connect with the leg (points A and B) and C is the center of gravity for the leg, located 2/3 L away from A. The angles from cable 2 is Beta=45 degrees.
    Find T1, T2, W1, W2, and the angle Alpha for the leg to stay in equilibrium.
    [PLAIN]http://img820.imageshack.us/img820/2055/drawing5.jpg [Broken]

    2. Relevant equations
    Sum of Fy=0
    Sum of Fx=0
    Sum of Moments = 0

    3. The attempt at a solution

    So I separated the pulleys, so have for the weight and pulleys on left:
    Sum of Fy= T1-W1=0
    For the weight and pulleys on right:
    Sum of Fy=T2-W2=0 (is this correct? What is the effect of the second pulley on the tension?)

    Sum of Fy= T1sin(Alpha) - W +T2sin(45)
    (Should these be T1sin and T2 sin or just T1 and T 2?)

    Then I did sum of moments:
    Sum of moments around point A = -W*2L/3 + T2sin(45)*L=0
    Sum of moments around C = -T1sin(Alpha)*2L/3 + T2sin(45)*L/3
    Sum of moments around B = W*L/3 + T1sin(Alpha)*L

    So basically I'm stuck. Not sure if so far it's correct of how to proceed.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 14, 2010 #2
    Can anyone help me out? Please.
  4. Sep 14, 2010 #3
    You have 5 unknowns so you will need 5 equations. Your moments all look okay to me, but your forces need some revision. You need to revise your Fy equation, and create an equation for Fx. Remember to use Newton's 3rd law to work out any kinks.
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