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Homework Help: A Mass Hanging From Multiple Strings

  1. Oct 20, 2008 #1
    A mass of 6 kg is hanging from a string, named string 3. The top of this string is connected to to other strings, string one which goes straight to the left to connect with a wall, and string two which connects to the ceiling making a 40 degree angle between the ceiling and the string. The problem is asking for the tension of string 2.
    The available answers are:

    EDIT: Will try and provide a picture when possible.

    a) 1.2 N
    b) 11 N
    c) 34 N
    d) 3.5 N
    e) 40 N


    I thought I could solve the problem by considering each string a vector, representing the force of each. Since there is no movement, the sum of the Forces should equal 0.
    So , T1+T2+T3=0

    I figure the force of T3 to be the F_g, which should be 6 *9.8=58.8 N

    Using this I then came up with the following
    T1*cos(180)+T2*cos(40)+58.8*cos(270) = 0
    and
    T1*sin(180)+T2*sin(40)+58.8*sin(270)=0

    I figured I could use the second equation most easily, since the sin(180)=0.

    So, I came up with 0+(.643)T2+58.8=0
    (.643)*T2=-58.8
    T2=-91.44
    Of course, this is nowhere close to any of the available answers, and I can't seem to wrap my head around any other way of doing it. Any help would be greatly appreciated.
     
    Last edited: Oct 20, 2008
  2. jcsd
  3. Oct 20, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Assuming your description is accurate, the available answers are way off.

    Your method is perfectly fine. You did make a sign error, but otherwise your answer is correct. (What is sin(270)?)
     
  4. Oct 20, 2008 #3
    Ahhh, yes, sorry, 58.8 * -1. Thank you for that. I guess I'll just have to discuss it with the teacher. Thanks!
     
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