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Homework Help: Balancing a spring and arm at 45 degrees

  1. Jul 13, 2012 #1
    I need to find what spring will balance an arm at 45 degrees
    the arm is 5m and can be considered as a UDL of 1.6kg/m
    the situation is that the arm starts upwards at 90 degrees and as it goes down it puts tension on the extension spring


    5*1.6 = 8kN
    acting 2.5m along the beam
    which is 1.77m in direction x (horizontal)
    8000*1.77 = 14160Nm (the moment acting at 45degrees)

    how do I find the details on the spring? (diameter, length etc)
    Maybe i'm approaching it wrong, any advice would be appreciated :)
     
  2. jcsd
  3. Jul 13, 2012 #2

    CWatters

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    What two points is the spring connected between ? Diagram might help.
     
  4. Jul 16, 2012 #3
    Here is what i mean
     

    Attached Files:

  5. Jul 16, 2012 #4

    CWatters

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    Ok. I reckon the spring needs to produce a torque about the pivot of

    = 8 * 9.8 * 2.5 * cos(45)
    = 138.6 NM

    PS: Normally we like you to have a go at the solution first.
     
    Last edited: Jul 16, 2012
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