1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating tension in each of 3 strings

  1. Oct 10, 2008 #1
    I have got a question i am having a lot of trouble with. The question is that three strings on unequal lengths are used to support a mass of 50g. All of these strings are used to support the weight. Two of these strings cannot be in the same plane as the other string. Determine the tension in each String.

    Well, i have 2 strings in the i and j plane and was thinking to have a third string in the k or k and j plane. However i do not know if this is correct. Also, could someone show me the general steps on how to calculate the tension in each string as i am having trouble with calculating this.
  2. jcsd
  3. Oct 10, 2008 #2
    It's going to depend exactly on how you define your planes and the angles that follow.
  4. Oct 10, 2008 #3
    well the planes are goin to be defined in terms of i, j and k.
  5. Oct 10, 2008 #4
    So you're putting the j plane parallel to the acceleration due to gravity?
    There are potentially infinite solutions to this question, I must be interpreting it incorrectly. Is that the exact wording of the question? Could you not have 1 string hanging from a ceiling straight down parallel to gravity, then two strings of equal tensions opposing each other perpendicular to the acceleration due to gravity?
  6. Oct 10, 2008 #5
    The strings have to be of unequal length though. And yes the j component is the same as y. (vertical)
  7. Oct 10, 2008 #6
    It gives no definition of where they have to be fixed though? The end that is not fixed to the mass I mean.
  8. Oct 10, 2008 #7
    its basically fixed to a wall or sumthing, so it must be fixed at both ends.
  9. Oct 11, 2008 #8
    any1? Its urgent. Thanks
  10. Oct 11, 2008 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Draw a freebody diagram.

    Fnet = 0 for x, y, and z directions.

    It depends on what angles the strings are oriented, which you know (hopefully) but we don't know.
  11. Oct 11, 2008 #10
    Heres a pic of 2 of the strings:
    http://img124.imageshack.us/img124/7268/25255782he6.th.png [Broken]http://g.imageshack.us/thpix.php [Broken]

    i just cant think of the length to place the third one in the k (or k and j) plane. Could u guys make sum suggestions and show me the process and calculations with ur sugeested length as i am having trouble calculating it. Thanks
    Last edited by a moderator: May 3, 2017
  12. Oct 12, 2008 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Yes, placing the 3rd string in the k-j plane would make sense. Are you free to choose the string lengths and angles? Making the arrangement as symmetric as possible is probably the best way to approach this, so perhaps making all 3 string lengths equal.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook