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Homework Help: Three forces in Equilibrium. Find the angles.

  1. Sep 30, 2008 #1
    I tried posting this once already; I don't know where it went. So here goes again.


    Three forces are acting on an object: 5.5N up and to the left; 6.1 N up and to the right; 9.3 N straight down. The system is in equilibrium.

    Find the angles from the horizontal axis to the two forces acting upward.

    2. Sum the forces in the x direction.
    Sum the forces in the y direction.

    Solve for one variable & sub into the other equation to solve.

    These problems are fairly easy to work when one or both angles are given. You can then find missing forces or angles. But this one asks for both angles. When you set the equations up, you end up with cos1, cos2, sin1, and sin2 as variables in your equations. Also each of the two equations has only sines or cosines in it but not a mix. I can't figure out how to sub back into the equation.

    Maybe this is simple and I just don't see it.

    (I did solve for the angles by setting up a combination of the equations and iterating. However, I don't think this is how it is supposed to be done. alpha1=51.03 deg, alpha2=55.45 deg.)

    View attachment homework attempt.pdf
  2. jcsd
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