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Homework Help: Could someone check me on this?

  1. Sep 1, 2005 #1
    OK, I have four forces in equilibrium

    F1 = 50i N

    e2 = -0.485i + 0.485j - 0.728k
    e3 = -0.557i + 0.743j + 0.371k
    e4 = -0.371i - 0.743j + 0.557k

    I need to find the magnitudes of F2,F3,and F4

    I got F2 = 373.67 N (this might be a + or -, not sure, thinking +)
    F3 = 346.43 N
    F4 = 102.44 N

    I used the equilibrium in each direction (x,y,z) and then I had three equations with three unknowns.

    If someone could confirm that or tell me where I messed up, that would be great. Thanks!
  2. jcsd
  3. Sep 1, 2005 #2


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    It's very tedious work to do manually. Hopefully for you, someone will check it using a math program. I suggest you get one of those and learn how to use it. Very usefull to check answers like this one.
  4. Sep 1, 2005 #3
    I have Mathematica, but I don't know how I would check it on there. Any thoughts?
  5. Sep 1, 2005 #4


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    If the body is in equilibrium under the action of no. of forces, then sum of their components in x,y and z direction separately is zero.

    If the force is given in the form
    F = Fx i + Fy j +Fz k then it means the Fx , Fy, Fz are components in the corresponding direction and the magnitude is given by sqrt(Fx^2 + Fy^2 + Fz^2)
    need not to solve the equations if the values are given.
    Last edited: Sep 1, 2005
  6. Sep 1, 2005 #5


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    He doesn't know the magnitude of F_2, F_3 and F_4. He known everything about F_1 and only the direction for the other 3. The directions are given by the unit vectors e_i.
  7. Sep 1, 2005 #6
    I solved the problem, I had a bunch of sign errors, but I fixed them.

    I used matlab to check it, but that was wrong. No worries, I am just saying.
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