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Homework Help: Tensions in cable

  1. Feb 26, 2010 #1
    1. The problem statement, all variables and given/known data

    http://img163.imageshack.us/img163/7491/staticsk.jpg [Broken]

    Those weird squiqqles are supposed to represent springs. Not exactly an artist :D

    2. Relevant equations

    F = kx

    3. The attempt at a solution

    After drawing a fbd and breaking the tension into x and y components I got:

    ΣFy T(sinθ) =5

    ΣFx T(cosθ) = T(cosθ)

    T = 5x since the force acting on the spring is T and k is given as 5.

    I tried taking the given 4ft into consideration, I tried seeing if there was some substitution I could make to solve any of those equations. Been struggling for like an hour now...
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 26, 2010 #2
    If the tension in the spring is kx, then the length of the spring is x+4 ft, because there's no tension if the spring is 4 ft long.

    Try to find another expression for [itex] sin(\theta) [/itex] or [itex] cos(\theta) [/itex] just from the goemetry.
  4. Feb 26, 2010 #3
    I should've been more clear. I used x to denote the amount the spring is stretched.. not the total length of the spring.

    And I have been trying for a while now. The only thing I can manage to do is sin/cos to get tan but I haven't done that in anyway that helps me out.
  5. Feb 28, 2010 #4
  6. Feb 28, 2010 #5
    you get a right-angled triangle with corners middle of the block, one end of the block, attachment to the load
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