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Homework Help: Tension of rope between two trees

  1. Jan 14, 2013 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    F = ma

    3. The attempt at a solution
    say I project the weight onto T
    then I get the right answer
    if theta = pi / 4 then Wcostheta = W / sqrt2
    but if I project the tension onto the weight, i dont get the right thing
    i get the opposite, Tcostheta = W
    which makes no sense
    i guess the question is
    is Wcostheta - T = 0
    or is Tcostheta - W = 0?
    which forces actually balance out
    im trying to see what balances out
    i mean its really intuitively obvious that Tcostheta - W = 0 should be true
    but that doesnt give the right answer
    its not accelerating vertically so Tcostheta - W = 0 should be true
    weird that it isnt
    i dont think weight is just W there
  2. jcsd
  3. Jan 14, 2013 #2


    User Avatar

    Staff: Mentor

    Two trees are supporting the weight of the rope. What does that tell you about the vertical component of the tension at each end? What then is the tension?

    At the midpoint of the rope only horizontal forces are acting in tension. The trees are providing the horizontal reaction force (equal and opposite, so nothing is moving). What's the horizontal component of the tension found above?
  4. Jan 14, 2013 #3
    Nvm, it's because I forgot to divide by 2
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