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!

Two hanging masses and three strings

  1. Jul 31, 2015 #1
    1. The problem statement, all variables and given/known data
    Two masses m and M (where M = 2m) are attached with strings. One mass m is suspended from a single verticle string held by two strings each at 45 degrees to the horizontal. The suspending string to the left at 45 degrees is attached to a fixed point. The string on the right at 45 degrees is attached to another mass M which in turn is attached by a further to a fixed point above at an angle theta to the horizontal.
    If the system is in equilibrium, determine the tension in the three strings in terms of m and g, and calculate the angle theta.



    2. Relevant equations
    F = ma

    3. The attempt at a solution
    As the system is in equilibrium i can say a=0 and therefore ΣF = 0.
    The y component of the two tensions in the two diagonal strings supporting mass m should be equal to mg when summed. Assuming the tensions are still equal (not quite sure what effect the other mass M would have on this - mass M is what has thrown me) then the tension in the bottom two strings should be mg/√2 ?
    The tension in the 3rd string connecting mass M with the fixed point ? My best quest was to say it is equal to √2mg as 2mg sin45 = T ?
    I also dont know theta however and dont see a way of finding it, at this point im almost sure i have absolutely none of this right! Any help on a method to solve this would be much appreciated!

    P.s sorry for the lack of image, cant seem to find anything on the web which shows a similar situation.
     
  2. jcsd
  3. Jul 31, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Good.

    Good.

    No need to assume that... prove it!

    Why guess? Apply ΣF = 0 to mass M and solve for the unknowns.

    You can use the whiteboard to slap something together yourself.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted