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Varrying load distance applies a two equal forces on two roller

  1. Oct 10, 2009 #1
    1. The problem statement, all variables and given/known data

    http://img198.imageshack.us/img198/374/20856431.jpg [Broken]

    2. Relevant equations
    Moment = R cross F
    Couple moments?


    3. The attempt at a solution

    I think I have to sum the moments from A, B and L all about C but I am not sure about the relationships between them.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 11, 2009 #2

    tiny-tim

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    Hi GarrettKoep! :smile:
    Yes, that's right …

    you know the directions of the forces at A B and L, but you have no idea which direction the force is at C, so the only sensible thing is to take moments about C. :wink:

    And since the angular acceleration is (obviously!) zero, that means that the sum of the torques (moments) must be zero.

    What do you get? :smile:
     
  4. Oct 11, 2009 #3
    After summing the moments about C I calculated that b=27
     
  5. Oct 11, 2009 #4

    tiny-tim

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    Hi GarrettKoep! :smile:
    (How did you get that? Anyway …)

    erm :redface: … when I said "you have no idea which direction the force is at C", I thought that the "pawl" was rigidly fixed to the rest of the body.

    But now that I've looked at the picture more carefully :rolleyes:, I realise that the pawl is loose … it can rotate freely at that unnamed point 8" up … let's call that point H.

    And since the pawl isn't rotating, that means that the force at C must balance the force at H.

    So we know the direction of both the forces at C and at H.

    And the rigid body is supported by forces at A B L and H.

    Use that information to find the direction and magnitude of the force at H, and then use moments to find b.

    Sorry I missed that point earlier. :redface:
     
  6. Oct 11, 2009 #5
    Okay, so if you calculated the sum of the moments about H the equation for b would change from (b-7)*L to (b-9)*L and they others would stay the same ( Fab *20). In conclusion, b would then be equal to 29.
     
  7. Oct 11, 2009 #6

    tiny-tim

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    If you want anyone to confirm that, you'll have to show your detailed calculations. :smile:
     
  8. Oct 11, 2009 #7

    nvn

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    GarrettKoep: Your current answer is incorrect. Try again.
     
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