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Homework Help: Finding Components of Force

  1. Nov 7, 2013 #1
    1. The problem statement, all variables and given/known data


    Force F acts perpendicular to the inclined plane ABC. Assume x0 = 2.32 m, y0 = 3.44 m, z0 = 2.94 m, and F = 459 N.
    Determine the moment produced by F about point B; What are the x,y,z component.

    2. Relevant equations

    Cross Product

    3. The attempt at a solution

    A (0,0,2.94)
    B (2.32,0,0)
    C (0, 3.44,0)

    rac = 3.44j -2.94k
    rbc = -2.32i + 3.44j
    rac x rbc = {10.1136,6.8208, 7.9808}

    uf = [rab x rbc]/[magnitude]={0.693785,0.467901,0.547477}
    F=459*uf = {318.545, 214.832, 251.112}
    mb = rbc * F = {864.44, 582.997, -1593.75}

    I am wrong. It has been hours. Any help would be great
    Last edited: Nov 7, 2013
  2. jcsd
  3. Nov 7, 2013 #2


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    What is the definition of a moment vector in terms of the force vector and the radius vector?
  4. Nov 7, 2013 #3
    Sorry can you explain further
    thank you
  5. Nov 7, 2013 #4
    Can someone spot out what I did wrong?
  6. Nov 7, 2013 #5
    The Rab and Rbc vectors are right, and so is their cross product, as well as the unit vector in the direction of the force. But I got 318.447i + 214.766j + 251.292k for the force vector. Oddly enough, I got the same moment though. Is the x, y, and z components at the end supposed to be the answer?
    Last edited: Nov 7, 2013
  7. Nov 7, 2013 #6
    Shouldn't the moment be rbc x F?
  8. Nov 7, 2013 #7
    Yeah that's what i did but I'm always wrong
  9. Nov 7, 2013 #8
    And yes gildomar, the answer is the components
  10. Nov 7, 2013 #9
    Wow, nevermind. I actually got it right.. I just kept on putting N instead of N*m.... im never taking physics again.

    thanks anyway
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