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Homework Help: Vectors Design Angle Problem

  1. Sep 10, 2014 #1
    1. The problem statement, all variables and given/known data

    "Determine the design angle θ (0° ≤ θ ≤ 90°) for strut AB so that the 400-lb horizontal force has a component of 500lb directed from A towards C. What is the component of force acting along member AB? Take ϕ = 40°"

    2. Relevant equations

    x-component: magnitude*cos(θ)
    y-component: magnitude*sin(θ)

    3. The attempt at a solution

    I understand what is being asked, I'm just unsure as to how I would get that AC component with what is given.


    Attached Files:

  2. jcsd
  3. Sep 10, 2014 #2


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    Staff: Mentor

    Hi Rybka. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    Please correct this.

    You have 3 forces, they must form a closed triangle. Struts exert their force in line with their length, so this tells you the directions of their contributions.

    Are you given the correct answer?
    Last edited by a moderator: May 6, 2017
  4. Sep 10, 2014 #3
    Good evening!

    The solution is: θ = 53.5°, ForceAB = 621lb
  5. Sep 10, 2014 #4
    I figured it out.

    The position of the struts in the first diagram is confusing, but the fact that we're solving for θ means their shape is variable.

    Once I moved things around a little bit, it all became clear. :smile:

    Attached Files:

  6. Sep 11, 2014 #5


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    Staff: Mentor

    It's always useful to know the answer. I was hoping you'd edit your post so it tells us exactly what is 40°. That would be useful for someone following along.

    Good to know you worked it out.
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