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Getting magnitude and direction of 3 forces

  1. Oct 18, 2013 #1
    I have completed this question but im not sure im right.

    3 co-planer forces acting at a point 0, 100KN→ at 0deg from o point, 70KN→120deg from o point and 50KN →210deg from o point (hope that make sense, cant draw it).

    using a scale of 10mm+10KN determine, By means of polygon of forces method magnitude and direction of their resultant.

    force--------Fx=fcosθ------------Fy=sinθ
    100KN----100cos0=100 ------100sin0=0
    70KN------70cos120=-35 ---- 70sin120=61
    50KN------50cos210=-43 ---- 50sin210=-25
    -------------------Ʃfx=22 ------------Ʃfy=36

    Resultant=42.19KN

    Tan-1=o/A=36/22=58.57deg
     
    Last edited: Oct 18, 2013
  2. jcsd
  3. Oct 18, 2013 #2

    Doc Al

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    Staff: Mentor

    Looks reasonable to me--except that the units are KN, not N. (You did it using components, but I suppose they wanted you to use a graphical method.)
     
  4. Oct 18, 2013 #3
    When I draw it on graph paper I measured the resultant and it was very close to the one I worked out,
    the angle on the other hand is off on the graph it 75deg.
     
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