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Homework Help: Centripetal Force Minimum Period Question

  1. Nov 14, 2012 #1
    1. The problem statement, all variables and given/known data
    A boy ties a 3.00kg rock to a 0.70 m string and begins spinning it around in a horizontal circle at a constant speed. If the string will break if the tension is greater than 80.0 N, what is the minimum period for the rock to spinning in a circle. How do i solve this?

    2. Relevant equations

    m4∏^(2 ) r/T^2

    3. The attempt at a solution
    80.0= (3.00)4∏^(2)(0.70)/T^2
    T= 1.02
  2. jcsd
  3. Nov 15, 2012 #2


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    Homework Helper

    Welcome to PF!
    Looks good. I get a very slightly larger answer; might be worth running it through the calculator again.
  4. Nov 15, 2012 #3
    Your equations written as pie squared r instead of pie r squared, i think you did it right but it looks weird
  5. Nov 15, 2012 #4
    its the equation in the text book. So can you explain how max tension gets minimum period?
  6. Nov 15, 2012 #5


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    Gold Member

    Yes, the equation is correct, though it does look odd at first sight.
    The stone has a certain distance to cover, 2πr, in one period. So minimum period means maximum speed, and that means maximum tension.
  7. Nov 24, 2012 #6
    Sorry your right, its so weird seeing pie digitally
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