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Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different angle

  1. Dec 16, 2012 #1
    1. The problem statement, all variables and given/known data
    The big sign below (see attached image) is 13 kg and the small sign is 4 kg. Find the tension in all 4 cables.


    2. Relevant equations
    Fnet= Fa +Fb


    3. The attempt at a solution
    ƩFx= T2cos38 - T1cos51=0
    T2=T1cos51/cos38
    ƩFy=T1sin51 + (T1cos51/cos38)sin38 - 127.4 -39.2 = 0
    T1=131.303
     

    Attached Files:

  2. jcsd
  3. Dec 16, 2012 #2
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    Your T2 is correct.

    T3 = T4 = 2g

    Fy: T1sin51 + T2sin38 = 17g

    this is because the only forces opposing the vertical components of the tensions are the weight of the 13kg and 4kg masses. So the only thing opposing the vertical components of the tension is a combined weight of 17kg which is 17g.
     
    Last edited: Dec 16, 2012
  4. Dec 16, 2012 #3
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    Thanks!
    Oh! And merry christmas
     
    Last edited: Dec 16, 2012
  5. Dec 16, 2012 #4
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    Hi, I've updated the post above, which might me helpful to you.
     
  6. Dec 16, 2012 #5
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    But the forces are in equilibrium and there is no acceleration so how can there be 17g? And won't the opposing forces be the weights, not the masses?
     
  7. Dec 16, 2012 #6
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    I think this is correct, I get the same:)
     
  8. Dec 16, 2012 #7
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    Just wondering...was my first attempt correct (my physics teacher posted the answer and her t1 was 131.18 N)
    I know I sound paranoid but still.... -_-
     
  9. Dec 16, 2012 #8
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    @ phizkid the "13 g" doesnt denote the mass, I think you mistook the g as a gram rather than the acceleration of gravity. Yoy're correct in mentioning that the system is motionless so that's why the net force is 0 for both the x and y components.
     
  10. Dec 16, 2012 #9
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    Oh ok then it's all the same
     
  11. Dec 16, 2012 #10
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    I get T1 = 131.3N

    We agree!
     
  12. Dec 16, 2012 #11
    Re: Tension problem dealing with 4 ropes and 2 weights (ropes oriented at different a

    "g" is not grams in this case, it is 9.8 m/s2. So by 17g I meant 17 x 9.8m/s2.
     
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