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Two strings spinning rock- tension

  1. Feb 6, 2009 #1

    TG3

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    1. The problem statement, all variables and given/known data
    A string 44 cm long will break under a tension of 24 N. Two such strings are tied to a 670 gm rock, their ends 60 cm apart. The rock is spun between them. What is the maximum speed it can spin before the string breaks?
    (Using pythagorean theorem, you can determine the radius of the circle is 32.187. I'll save you the hassle.)


    2. Relevant equations
    N = m (v^2 / r)


    3. The attempt at a solution
    48 =.67 x (v^2 / 32.187)
    71.64 = v^2 / 32.187
    2305.934 = v^2
    48.020 = v

    I have a suspicion that the problem is conceptual: am I supposed to use sine or cosine somewhere?
     
  2. jcsd
  3. Feb 6, 2009 #2
    Draw the diagram of forces and you'll see that the tension in each string can be divided into two components. One component supplying the centripedal force to the stone, and one pulling on the other string.

    So your line
    48 =.67 x (v^2 / 32.187)
    needs modification.
     
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