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Homework Help: Window Washer Torque problem

  1. Dec 19, 2004 #1
    A scaffold of mass 68 kg and length 6.1 m is supported in a horizontal position by one vertical cable at each end. A window washer of mass 77 kg stands at a point 1.7 m from one end.
    What is the tension in the cable closer to the painter?
    What is the tension in the cable further from the painter?
    I calculated two forces 543.5 and 877.5, Im just not 100% sure what end each one is.
  2. jcsd
  3. Dec 19, 2004 #2
    Why don't you explain what you did. Its easier to determine if you are right that way.
  4. Dec 19, 2004 #3
    I did it really quickly, and your answers seem right. In terms of determining which is which, be consistent with your variables and it should work out.
  5. Dec 19, 2004 #4
    I first converted calculated the Force Weight because the answer needs to be in newtons. Then I put a pivoit on the side closest to the window washer and balanced the forces.
    (754.6 * 1.7) + (666.4 * 3.05) = 6.1x
    543.5 = x
    Then I subtracted that from the total downward force of 1421 to find the other side at 877.5
    Im just not sure which side has what force.
  6. Dec 19, 2004 #5
    No one knows this? I really need to do this soon.
  7. Dec 19, 2004 #6
    Just take the moment at each end. Each one is only one equation one unknown.
  8. Dec 19, 2004 #7
    Also, just looking at what side the window washer is on, you should intuitively determine which side will have more tension.
  9. Dec 19, 2004 #8
    Label the force on the left side as T1 and the force on the right as T2. Then place the person somewhere on the bar. If you draw your free body diagram properly and are consistent with your variables you should be able to see which side is which.

    You can also do it intuitively as Cantari suggested. Based on where the person is standing, which side do you think will have more tension?
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