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Homework Help: How far away from its location when the string breaks

  1. Feb 18, 2013 #1
    1. The problem statement, all variables and given/known data
    A 4-kg rock is tied to the end of a string and twirled overhead, 1.6 m above the ground, in a 1.1-m radius, horizontal circle. The string is known to break if its tension reaches a value of 514 N. The rock it rotated faster and faster until the string breaks. How far away from its location when the string breaks will the rock hit the ground? Your answer should be given in meters, to the nearest centimeter.

    2. Relevant equations

    3. The attempt at a solution

    What I did was I found V first by doing sqrt(f*r/m)
    Then I found t by doing sqrt(2y/g)
    then I multiplied vt.

    I've tried this three times and I keep getting this answer wrong. On my last attempts i've been getting between 6.9m and 7.1m based on the configuration of the numbers as they change slightly each time I attempt the problem.

    What am I doing wrong?

  2. jcsd
  3. Feb 18, 2013 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    I think you should go into more detail about your reasoning.
    However, the thing that jumps out at me is that you appear to have assumed that the tension in the string is the only force on the rock while it is being twirled around the circle.
    i.e. in
    How did you find "f"?
    Last edited: Feb 18, 2013
  4. Feb 18, 2013 #3


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    Staff Emeritus
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    One seems to have the appropriate equations, but the circular trajectory of the rock is horizontal, not necessarily the string.

    What are the time to fall and the linear speed at which the string breaks?
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