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Homework Help: Statics/Moments - Force perpendicular to slope?

  1. Oct 6, 2012 #1
    Determine the resultant moment at support points A and B due to the forces acting on the truss as shown.

    Fx = F(cos∅), Fy = F(sin∅), M = F(distance)

    Point A -88.98kN*m
    Point B ?

    I have no problem calculating most of the forces, but I'm lost when it comes to knowing what to do with the forces that are perpendicular to the sloped surfaces. Do I calculate X and Y components for them? Does it automatically turn into an X or Y component? When trying to calculate the moment on point B, is the 10kN multiplied by zero because it's on the same x-axis as the point, or is the 10kN a Y component? Some insight would be hugely appreciated.

    Attached Files:

  2. jcsd
  3. Oct 6, 2012 #2
    Yes, for any forces that are at an angle, generate the x and y components of the force. And good catch, the 10kN force will be multiplied by zero because it is on the same x-axis as point B (when calculating the reaction at B). However, only the x-component of that force is neglected in the calculations, be sure to include the y-component.
  4. Oct 6, 2012 #3
    I figured it would still require the X and Y components! Which angle would I use to calculate those?
  5. Oct 6, 2012 #4
    The angle should be 45degrees so the x-component is 10cos(45) and the y-component is 10sin(45). At least I hope it is haha.
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