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Homework Help: 3-D Statics Problem

  1. Sep 6, 2011 #1
    1. The problem statement, all variables and given/known data

    [PLAIN]http://img846.imageshack.us/img846/6546/statics.png [Broken]

    2. Relevant equations

    Fy = F*cosθy
    Fh = F*sinθy

    Fx = Fh*cosφ = F*sinθy*cosφ
    Fz = Fh*sinφ = F*sinθy*sinφ

    3. The attempt at a solution

    I'm having a lot of trouble drawing vector AD in a free body diagram. I think I need to draw one as that will help me further understand the solution that is worked out. I'm just having trouble identifying the angles that I should utilize and where on the diagram they should be placed. If someone could possibly draw up a diagram that helps with identifying what is what that would be very helpful.

    Fy = F*cos30
    Fh = F*sin30

    You could say my main problem is identifying which is φ, I just cannot tell from the picture at all. What exactly is φ defined as, my book's definition is pretty vague.

    Or am I going about this the wrong way?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 7, 2011 #2


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    Science Advisor
    Homework Helper

    Hi VitaX! :smile:
    φ is the angle from the x-axis (in the x,z plane) :wink:

    since the tension has to be along AD,

    the easiest way to do this is to use O as the origin and to find the (x,y,z) coordinates of A and D …

    then the vector (D - A) is the one you want, and you can find the angles by "dotting" it with each of the three unit vectors along the axes :smile:
  4. Sep 8, 2011 #3
    Ok thanks for that, determined it to be 40 degrees. Was finally able to get a good drawing of it.
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