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Homework Help: Statics - mass attached to a string. Find forces acting to keep in equilibrium!

  1. Feb 22, 2010 #1
    Hey guys, this is my first time posting and I really need your help.

    I'm stuck on this question:
    A light inextensible string of length 40cm has its upper end fixed at a point A, and carries a mass of 2kg at its lower end. A horizontal force applied to the mass keeps it in equilibrium, 20cm from the vertical through A. Find the magnitude of this horizontal force and the tension in the string.

    From this I think I only know one force which would be 2g. I also know the lengths but what to do with them?!
    I'm guessing I have to use trigonometry? I'm really clueless and don't know where to start. I can't even think of what the diagram would look like. I'd appreciate any help!

    I tried making a triangle, with sides 0.2,0.4 and 2g. Don't know how this will help tho :(

    Thanks in advance
  2. jcsd
  3. Feb 22, 2010 #2


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    Homework Helper

    Hi HM, welcome to PF.
    40 cm, 20 cm and vertical forms a right angled triangle. From that you can find the angle between the horizontal and the tension in the string. Then find the component of T in the vertical and horizontal direction. Equate the vertical component to mg and the horizontal component to force. And solve for F and T.
  4. Feb 22, 2010 #3
    Thanks a lot for the help.I followed your instructions and got T=22.6N and F=11.3N which are the answers in the back!!!

    Cheers :)
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