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Homework Help: Calculating tensions in ropes suspending an onject

  1. Jun 11, 2017 #1
    1. The problem statement, all variables and given/known data
    A mass of 20 kg is suspended from a ceiling by two lengths of rope that make angles of 30° and 45° with the ceiling . Determine the tension in each of the strings.

    2.Relevant equations

    Fg= mg

    3. The attempt at a solution
    Fg= 20 x 9.8 = 196 N

    ∑F= fnet=ma
    Fg-FTtotal= 0
    196= FTtotal
    196= FT1y+ FT2y (y components of each of the tensions)
    196= (cos60)(FT1) + (cos45)(FT2)
    I think I'm doing something wrong and I dont knownwhat. In the textbook, instead of using the y components of the tensions, they just use the tensions, which doesnt make sense to me because it's the y components of the tensions that give the equilibrant force to Fg.
  2. jcsd
  3. Jun 11, 2017 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What you're doing is fine, but don't forget the x-components. That will give you the second equation that you need to solve for your two unknowns.
  4. Jun 11, 2017 #3
    Ohhhhh right! I forgot about that! And then it's substitution and stuff from there, thank you!
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