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Homework Help: Force that Maintains Circular Motion

  1. Apr 9, 2010 #1
    1. The problem statement, all variables and given/known data

    A string with the length of 4.23 m can support a weight of 25 g. If you add a weight and spin the string horizontally above your head, it breaks upon reaching a tangential velocity of 5.1 m/s. What is the mass of the weight?

    so... radius=4.23m, V(t)=5.1 m/s, and mass=unknown

    2. Relevant equations

    Angular Displacement = (arc length) / (radius)
    Centripetal Force = (mass)(tangential velocity)(tangential velocity) / (radius)
    Centripetal Force= (mass)(radius)(angular speed)(angular speed)
    Tangential Velocity=(angular speed)(radius)

    3. The attempt at a solution

    I'm not quite sure which equations pertain to solving this type of problem, but I don't know where to get started when you're not given the value of the centripetal force... Any help would be greatly appreciated! Thanks!
  2. jcsd
  3. Apr 9, 2010 #2
    a = v^2/r, for centripetal motion.

    Then use that acceleration value to relate the opposing forces. The tension in the string and the acceleration of the weight. A newton's second type equation. Solve for the mass. Total F = T - ma = 0
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