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Homework Help: Simple Loading System

  1. Mar 28, 2010 #1
    1. The problem statement, all variables and given/known data

    The question is fairly easy, however the way they want the answer displayed is doing my head in.. Anyways the questions states

    "replace the loading system by an equivalent resultant force (express your answer in terms of the unit vectors i and j)"

    The question is a simple beam with forces along different sections, refer to the image I've uploaded to see what I'm talking about.

    3. The attempt at a solution

    I know that the resultant Force lies along the beam at the 2metre mark and the force at this particular point, is 6.25kN I believe...

    Any help is greatly apprechiated, I'm a little new to the whole vector thing, so forgive me. Thanks in advance


    Attached Files:

  2. jcsd
  3. Mar 28, 2010 #2


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    Homework Helper

    Well if you move a load to the centroid, you get the force at the centroid and a resulting moment.

    So if you move the 2.5kN to the 2m mark, you will get a clockwise moment of 6.25kNm.


    But I too am not sure about how they want the answer expressed. (with respect to the i component that is)
  4. Mar 28, 2010 #3
    Hi thanks for the reply, I understand that if I move 2.5kN to the 2m mark, I will get a clockwise moment of 6.25kNm. However the question asks me to "Express my answer using the unit vectors i and j" How would I express 6.25kNm into its appropriate unit vectors?
  5. Mar 28, 2010 #4


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    The 6.25 is in the j direction
  6. Mar 29, 2010 #5
    Ah Thank you so much. The answer was j(6.25) kN. Life savers :D
  7. Apr 5, 2010 #6
    what was the answer to this question? j(6.25) doesn't seem right to me
  8. Apr 5, 2010 #7
    the answer to this was Fr = vector J (-6.25)kN.
  9. Apr 5, 2010 #8
    didn't u need to express a value for i? like 0i-6.25j?
  10. Apr 5, 2010 #9
    I suppose you could... Are you doing the same question in mastering engineering or mastering physics?
  11. Apr 5, 2010 #10
    mastering engineering
  12. Apr 5, 2010 #11
    all my answers are getting rejected for some reason, is there something i'm missing? :S
    Last edited: Apr 5, 2010
  13. Apr 5, 2010 #12
    Have a look at that attached image of mine... Maybe that can help you.

    Attached Files:

    • a.png
      File size:
      18.4 KB
  14. Apr 5, 2010 #13
    Nvm i got it, was entering unit wrong.
    Last edited: Apr 5, 2010
  15. Apr 5, 2010 #14
    hahah no worries man, should of mentioned that you needed to select the vector button :S. Module 3 is looking fun ay :D
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