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Are my answers correct? (3D statics)

  1. Jul 1, 2011 #1

    Femme_physics

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    I don't have the solution manual answer for this problem, can anyone help please confirm my answers are correct?

    1. The problem statement, all variables and given/known data


    http://img860.imageshack.us/img860/6118/40893341.jpg [Broken][/QUOTE]

    On a smooth horizontal weightless surface ABDC acts at the center a vertical force of 600 [N]. The surface is connected to the wall through axes A and B and supported by shaft CE.

    A) Calculate reaction at CE
    B) Calculate reactions at axes A and B. Presume the forces at the B axis are at the X and Y direction only.


    3. The attempt at a solution

    This is my solution attempt

    http://img204.imageshack.us/img204/2712/20112011a.jpg [Broken]

    http://img834.imageshack.us/img834/6539/20112011b.jpg [Broken]]


    And here below in the thumbnail I have attached my friend's attempt. He's smart, but new to 3D statics, and I don't understand how what he did makes sense. In fact it contradicts my results and methods.
     

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    • sp2.jpg
      sp2.jpg
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    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 1, 2011 #2

    I like Serena

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    I don't understand what your friend did.
    It looks rather complex, but his answers are wrong.

    I definitely prefer your method. :smile:
    Reducing the problem to 2D makes it much easier to follow what you did.

    However, you also made a mistake.
    It starts with your zx-view, when you calculated TCEzx where you used TCEy, but you should have used TCEx.
    Same for the calculation of TCEz.

    As a consequence, your Bx, Ax, and Az are wrong too.
     
    Last edited by a moderator: May 5, 2017
  4. Jul 1, 2011 #3

    Femme_physics

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    *smacks forehead*

    I'll tell you why, I'm used to "y" being up so I keep confusing myself :tongue:


    Thanks a bunch :smile: will correct it today
     
  5. Jul 2, 2011 #4

    I like Serena

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    But "y" is up!!! :confused: :tongue2:
     
  6. Jul 2, 2011 #5

    Femme_physics

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    It's "up" in the 3D drawing. But in the 2D ones, it's always psychologically my "up"-- something which I still haven't completely gotten rid off.
     
  7. Jul 2, 2011 #6

    I like Serena

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    Uhh, it's up in 3D and it's up in your yx-view and it's up in your yz-view. :uhh:

    It's just that in 3D normally z is always up, and in the yz-view z should be up too! :smile:
     
  8. Jul 2, 2011 #7

    Femme_physics

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    Yes, I said psychologically "up" as in the sense that's it's pointing towards the upper part of the page that I'm writing on heh, I still haven't gotten over it is what am saying
     
  9. Jul 2, 2011 #8

    I like Serena

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    Still, in this problem y is pointing up to the physical top of your page.

    I think you've gotten over that just fine! :smile:
    You're already used to the fact that z should be pointing up to the physical top of your page.

    The challenge in this problem is to apply the direction of the y-coordinate mathematically, carefully without making assumptions based on the 3D you're already used to.
    That really makes this problem harder than it has to be. :wink:
     
  10. Jul 2, 2011 #9

    Femme_physics

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    not if you're looking at the xz view
     
  11. Jul 2, 2011 #10

    I like Serena

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    *smacks forehead*

    Oooooooooooooooooooooooh!
    (Thanks for clarifying that! :wink:)
     
  12. Jul 2, 2011 #11

    Femme_physics

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  13. Jul 2, 2011 #12

    I like Serena

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    Yay! :smile:

    You didn't ask for it, but I give it the ILSe-stamp-of-approval.
    Btw, whatever happened to that item that I didn't put a stamp-of-approval on? :blushing:
     
  14. Jul 2, 2011 #13

    Femme_physics

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    Maybe I didn't ask, but I secretly desired! :wink:
    Thanks :mrgreen:

    "Btw, whatever happened to that item that I didn't put a stamp-of-approval on?
    "

    To be amended, rest be assured! :smile:
     
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