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Homework Help: Having trouble with this Moments about the coordinate axes problem!

  1. Sep 23, 2010 #1
    Having trouble with this "Moments about the coordinate axes" problem!

    When a force F is applied to the handle of the valve shown, its moments about the x and z axes are, respectively, M_x= -77 lb ft and M_z= -81 lb ft. For d=27 in., determine the moment M_y of F about the y axis.
    [PLAIN]http://img411.imageshack.us/img411/8366/092310015800.jpg [Broken]

    I figure I'm supposed to use the formulas:

    M_x= yF_z - zF_y
    M_y= zF_x - xF_z
    M_z= xF_y - yF_x

    but I'm having trouble on finding a component of the force.

    Also, are my x,y,z's correct??

    I got, x=-4, y=11, z=-27

    Thanks!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 23, 2010 #2
    Re: Having trouble with this "Moments about the coordinate axes" problem!

    Sorry for the large picture, right click>view image for a better view of it!
     
  4. Sep 26, 2010 #3
    Re: Having trouble with this "Moments about the coordinate axes" problem!

    im working on this same problem and i cant figure it out at all. all i know is that your x,y,and zs are wrong. you are given the moments with units of ft.*lbs. and those numbers are inches, so you need to divide them by 12 to make them feet.

    i managed to express M_y in terms of F_y but idk how to solve for F_y. its still in terms of F and theta. there must be more equations to use that we arent thinking of.
     
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