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Two masses connected by a string uniform circular motion. HELP!

  1. Nov 8, 2011 #1
    Two masses connected by a string uniform circular motion. HELP! :)

    1. The problem statement, all variables and given/known data
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    A puck of mass m1 is tied to a string and allowed to revolve in a circle of radius R on a frictionless, horizontal table. The other end of the string passes through a small hole in the center of the table, and an object of mass m2 is tied to it. The suspended object remains in equilibrium while the puck on the tabletop revolves.

    What is the tension in the string? (Use any variable or symbol stated above along with the following necessary: g.)

    So. I keep looking at this problem...there's more questions to this but the first part is stopping me from completing the others. I was wondering how does the mass m2 effect the tension in the string if it is stationary? I know the tension for mass m1 by itself would simply be T=m1v2/R. Also that if I isolated mass m2 the tension would simply be T=m2g. How do I incorporate them or is one case null? Any suggestions? Thank you :)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Nov 8, 2011 #2
    Re: Two masses connected by a string uniform circular motion. HELP! :)

    You have it sorted out!
    The tension needed to keep m1 in circular motion is m1v^2/R. This is the centripetal force.
    This force is provided by the WEIGHT of m2 =m2 x g.
    Think of Newton's 3rd law. If the string is pulling on m1 with a force F then the string must be pulling on m2 with a force F. (remember there is no friction to worry about)
     
  4. Nov 8, 2011 #3

    Simon Bridge

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    Re: Two masses connected by a string uniform circular motion. HELP! :)

    You got it - both expressions have to be correct.
    However, one of them uses a variable or symbol not supplied and you are restricted by the terms of the question to use only those which are supplied.
     
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