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Tension: 2 wires one at 60degrees one at 45degrees

  1. Jan 20, 2013 #1
    How do you solve for tension, is there a general formula to use

    for emample such as this problem(this is not homework, its an example i saw )

    you have 2 wires one at 60degrees one at 45degrees both wires have a weight of 5N. find the weight of the third wire thats going down?

    how does one approach such a problem

    I tired doing this , this way, but i' am wrong since the right answer is 6.1N

    1. ||a||5Ncos60=||b||5Ncos45
    2. ||a||5sin60+||b||5sin45=c

    I substituted equation one into 2 and i got 6.9N
     
  2. jcsd
  3. Jan 20, 2013 #2

    SteamKing

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    Your problem statement is a bit confusing. For example, the reference of the angles is ambiguous. Are the angles measured with respect to the vertical or horizontal?
     
  4. Jan 20, 2013 #3

    haruspex

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    Do you mean the wires have a tension of 5N?
     
  5. Jan 20, 2013 #4
    horizontal
     
  6. Jan 20, 2013 #5
    \*****/each wire here has 5N of tension
    *\***/
    60 \*/45degress
    ***|
    ***|
    ***|
    ***? what the weight here?
     
  7. Jan 20, 2013 #6

    haruspex

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    Your third wire cannot be vertical. All you need to do is find the resultant force from the upper two wires. The force from the third must balance that.
     
  8. Jan 21, 2013 #7

    tms

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    But if we're talking wires, it pretty much has to be vertical. I think something is missing from the statement of the problem.
     
  9. Jan 21, 2013 #8

    haruspex

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    If we're talking hanging weights it has to be vertical, but then the provided information would be inconsistent. I'd say we're just talking tensions, so the wire can be any angle.
     
  10. Jan 21, 2013 #9

    tms

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    But the third wire is just a hanging weight, according to the information given by the OP. I see what you mean, though, about assuming that the third wire is connected somewhere; the OP could have misunderstood the actual problem, or I could have read too much into the given information.
     
  11. Jan 21, 2013 #10

    haruspex

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    All three were described as 'having a weight' (not, e.g., 'having a weight attached'). So I feel the most likely intended meaning is that each has a tension.
     
  12. Jan 21, 2013 #11

    tms

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    You're probably right.
     
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