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Winch Puller Statics

  1. Sep 14, 2009 #1
    1. The problem statement, all variables and given/known data

    It is known that a force with a moment of 960N*m about D is required to straighten the fence post CD. If d=2.8 (already replaced), determiethe tension that must be developed in the able of winch puller A o create the reuired moment point D.

    Statics3.jpg

    2. Relevant equations
    W=Fd
    Fx=Fcos(theata)


    3. The attempt at a solution

    Fx=TAB*sin(17.78)
    Fy=TAB*cos(17.78)

    MD=TAB*sin(17.78)

    960=TAB*sin(17.78)*.898m
    TAB=1122 N

    Answer is:1224 N

    but how?
     
  2. jcsd
  3. Sep 14, 2009 #2
    any ideas would be great!
     
  4. Sep 14, 2009 #3

    Redbelly98

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    You're looking for the torque, or moment-arm, about point D due to the rope tension. There should be a formula in your book to calculate this, it will involve force, distance, and an angle -- but it's not the equation for work that you quoted.
     
  5. Sep 14, 2009 #4
    thats the equation for a moment about D
     
  6. Sep 14, 2009 #5
    in my book it even stats that instead of putting the normal units for work I should put N*m.
     
  7. Sep 15, 2009 #6

    Redbelly98

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    Yes, exactly. You need the moment arm, due to the cable, about D. In other words, the perpendicular distance from D to the cable.

    That's right.
     
  8. Sep 15, 2009 #7
    Statics3-Work.jpg

    I got .898 because that is the height of the pole. Since the force for the x direction makes the system go counterclockwise it is positive. The force in the y direction is non exsistent because it goes along the line of action so if i push straight down on the pole it doesn't move. The angle at A is the same as the angle of the force. So why doesn't my work work?
     
  9. Sep 15, 2009 #8

    Redbelly98

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    Draw a line from D to the cable, perpendicular to the cable. That is the distance to use for calculating torque.
     
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