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Tension woes simple mass problem

  1. Oct 9, 2008 #1
    I thought I had this stuff figured out, but my answer is wrong. Any tips?
    Thanks

    1. The problem statement, all variables and given/known data

    A sign hangs precariously from your prof's office door. Calculate the magnitude of the tension in string 1 if theta-1 = 26.10degrees, theta-2 = 54.87degrees, and the mass of the sign is 6.50 kg.

    [​IMG][​IMG]

    2. Relevant equations

    [tex]\sum[/tex]Fx = T1x - T2x = 0
    [tex]\sum[/tex]Fy = T1y + T2y - Fg = 0
    Fg = mg

    3. The attempt at a solution

    X components:

    T1x = T1 Cos 26.1
    T2x = T2 Cos 54.87

    Y components:

    T1y = T1 Sin 26.1
    T2y = T2 Sin 54.87

    [tex]\sum[/tex]Fx = T1Cos 26.1 - T2Cos 54.87 = 0
    So...
    T1Cos 26.1 = T2Cos 54.87
    T1 = T2(Cos 54.87/Cos 26.1)

    and

    [tex]\sum[/tex]F = T1Sin 26.1 + T2 Sin 54.87 = (6.5 kg)(9.8 m/s2)

    Then I tried plugging that T1 in there...

    T2(Cos 54.87/Cos 26.1)Sin 26.1 + T2Sin 54.87 = 24.7 N
    T2(0.6408)Sin 26.1 + T2Sin 54.87 = 24.7 N
    T2(0.2819) + T2(0.8178) = 24.7 N
    T2(0.2819 + 0.8178) = 24.7 N
    T2 = 22.5 N

    I can't attempt any more solutions as the assignment was due 20 minutes ago (it's online)... but I did poorly on my midterm yesterday so I really need to get a better understand of the material before it's too late... any advice would be greatly appreciated!
     
  2. jcsd
  3. Oct 9, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Your method looks fine, just be careful with the arithmetic: 6.5*9.8 ≠ 24.7.
     
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