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Homework Help: Statics advice please?

  1. Dec 10, 2011 #1
    Physics advice please?
    If a question was to ask, calculate the maximum bending moment

    Could I find out the shear force points and graph it, then calculate and plot the bending points and manually find the max by observing the highest peak or is there an equation I should use?

    The beam is 3 meters long. Simply supported at either end and carries two point loads, one at 1m (5kn) and the second at 2m (10kn). No u.d.l

    Can someone advise me of the best way. Bearing in mind the question says calculate?

    For my resistance I get x1 to be 6.7kn and x2 at 8.3kn.

    For my shear force diagram I get +6.7 for m1, +1.7 for m2 and -8.3 for m3

    Bending diagram I get at m1 to be +6.7, m2 to be +8.4 and m3 to be +0.2

    Am I correct so far or have I over complicated things when I could have used an equation?
  2. jcsd
  3. Dec 10, 2011 #2


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    charger9198: Nice work. However, the unit symbol for kilonewton is kN, not kn. Lowercase n means nano. Also, always leave a space between a numeric value and its following unit symbol. E.g., 10 kN, not 10kN.

    Generally always maintain at least four significant digits throughout all your intermediate calculations, then round only the final answer to three significant digits. E.g., 6.667 kN, not 6.7 kN. Your numbers are too rounded, and this may have caused your final answer to be slightly inaccurate. Also, points are usually labeled with letters (A, B, C, D), so I do not really know what you mean by m1, m2, m3.

    From your plot, you can manually see that the maximum bending moment occurs at point C. Therefore, you can compute the maximum bending moment at point C (as I think you already did). Except round it to three significant digits of precision, not two. Also, your moment at point D is currently incorrect.
  4. Dec 11, 2011 #3
    nvn: Many thanks for the advice, i re-calculated accordingly and seemed to get more accurate answers
    A= +6.667 kN
    B= +8.334 kN
    c= +0.001 kN

    I shall draw the shear force and bending moment diagram inline with the given and show the maximum bending moment to be +8.334 kN 2m from point A
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