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Moment in different dimensions in 2 D

  1. Dec 1, 2014 #1
    1. The problem statement, all variables and given/known data
    This isn't exactly a HW question, it's a question in my statics midterm today, he wants the reactions at the supports B and C, which is easy but the problem is this 60 N.m moment, all my friends were like :" lets just sum the moments around B ( due to the 50 N and the reaction at C) and just add this 60 N.m, but when i tried it , the reaction at C was 1100 N , which is kinda huge , plus , i don't think we can just add them , as the dimension of the moment created by the 50 N and the reaction at C is in the k direction while the 60 N.m ( using the right hand rule) should be in the i direction, so i don't think we can just add them up
    so, who's right? add them or don't add them?

    2. Relevant equations


    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Dec 1, 2014 #2

    haruspex

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    While the diagram does make it look as though the 60N.m is twisting the structure out of the page, that doesn't make much sense mechanically. There is no countering torque. So I suspect it is intended to be in the k direction. Any wording in the question that might clarify?
     
  4. Dec 1, 2014 #3
    the wording was , find the reaction at B and C if a = 1.5
    makes no sense if this was in the k direction, because, why would he even draw it there, the moment in the K direction is drawn 99% of the times around one of the supports
     
  5. Dec 1, 2014 #4

    haruspex

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    Are you saying the text does not mention this extra 60 N.m torque at all?
    I agree there is no interpretation that makes much sense. It could be intended to be some external torque about B, but in that case it is drawn strangely and I would expect it to be mentioned in the description. If it is in the k direction it swamps the 1.5 N.m from the load at A. I'd be inclined to dismiss it as either a mistake in the diagram or (as a torque in the i direction) as a deliberate red herring.
     
  6. Dec 1, 2014 #5
    my interpretation is : this question is from a text book , where they often use the same figure for different questions, maybe it's used in another question, in the exam, i tried to add it, made no sense with the 1100 N reaction at C
     
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