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Finding an angle with Newton's Second Law

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  1. Oct 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Given the free-body diagram below, and that the body is in equilibrium, find θ.
    ee3VjBf.jpg
    2. Relevant equations
    F = ma

    3. The attempt at a solution

    Basically, I used newton's second law in the y direction.

    Here is my work:
    o4KjcyS.jpg
    This does not seem like the correct answer, because the angle is acute. Thus, what am I doing wrong?
     
    Last edited: Oct 26, 2015
  2. jcsd
  3. Oct 26, 2015 #2

    SammyS

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    First of all, the three forces may have equal magnitude, but they are not equal as vectors.

    That should be cos(θ/2) or equivalently sin(90° - θ/2)
     
  4. Oct 26, 2015 #3
    So θ = 120 degrees?
     
    Last edited: Oct 26, 2015
  5. Oct 26, 2015 #4

    SammyS

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    Yes.
     
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