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Pulley Hoist Free Body Diagram

  1. Mar 5, 2013 #1
    Hi All,

    I am an old dog, and rusty propeller head. I am having the most difficult time figuring out the forces on a pulley system I am working on. Can someone please review my sketch and tell me if I am even close. I would accept any suggestions and direction.

    Much Obliged
    -Steve
     

    Attached Files:

  2. jcsd
  3. Mar 5, 2013 #2

    mfb

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    How can you support W/2 with two strings of W/8 tension (in addition, they have some angle between them!)
    In addition, what happens to the end of the string (right side)? I think it should help to support the weight, too.

    W/8 is a force, the tangent of a force is not well-defined.
     
  4. Mar 5, 2013 #3
    Yes, I knew my W/2 did not add up correctly with 2 - W/8 loads. That is really where I need help.

    W = Load
    W/2 is a pulley at each end of the W
    The angle is not counted at this time to avoid further confusion.
    The end of the string is lifting W
    I drew the tangent of middle pulleys for reference. The load on them will not affect my system I am building. I can calculate the load after I correctly figure out the force multiplier of my pulleys.

    I hope I helped clear some up your questions.
     
  5. Mar 5, 2013 #4

    mfb

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    The end of the string is lifting the same as all other parts. If we approximate that those string elements are vertical, we have 5 times the string tension holding that weight W, so string tension is W/5.
     
  6. Mar 5, 2013 #5
    Thank you,

    So that I have more understanding...

    Is the weight only carried by the string between pulleys B-C, C-D, G-H, H-I , I-to end?

    Also; Is my W/2 at pulleys C and H correct?

    Do I substitute W/5 for where I have W/8 throughout the string?

    -Steve
     
  7. Mar 6, 2013 #6

    mfb

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    As the other parts are not connected to the weight... sure.
    No, as you did not consider the end here.
    Right
     
  8. Mar 6, 2013 #7
    Thank you !

    I believe I have all that I need.

    Peace.
     
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