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Homework Help: Forces In Equilibrium

  1. Aug 13, 2009 #1
    1. The problem statement, all variables and given/known data

    http://img31.imageshack.us/img31/3926/71072701.jpg [Broken]

    I need to find the value of F2. I have drawn the free body diagram, and to find F2,

    F2 cos 30 + F3 sin 30 = 10N
    F1 cos 30 + F2 sin 30 = F3 cos 30

    I used this method, and tried to solve it but it doesn't lead me to the answer. Anyone can guide me? Thanks.

    2. Relevant equations

    3. The attempt at a solution
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Aug 13, 2009 #2
    Rotate your axis so that the F1 and F3 are exclusively in the x plane. From there it should be easy. You know the force of gravity, and you can find it's i and j components and solve for the rest. That's the trick to these inclined plane problems -- choose your axis wisely.
  4. Aug 13, 2009 #3


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    First draw yourself a coordinate system (x and y axes) so that we can talk about components of vectors. For a problem of this sort, x is usually along the incline and y perpendicular to it.

    Once you've done that, find the components of each vector. Since the object is at rest, the sum of all the x components must be zero and the sum of all the y components must be zero.

    Note that for a sum of two terms to be zero, one term must be positive and the other negative. Your equations do not show that, With a coordinate system drawn, it should be easy to see which components are positive and which are negative.
  5. Aug 13, 2009 #4
    Thanks a lot guys. I've got it.
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