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Breaking tension, and a weight component

  1. Oct 20, 2008 #1
    I have 2 questions, here is the first:

    1. The problem statement, all variables and given/known data
    A 1.31kg mass attached to a light string rotates on a horizontal, frictionless table. The radius of the circle is 0.402m, and the string can support a mass of 34.6kg before breaking.
    The acceleration of gravity is 9.8ms^2.
    What maximum speed can the mass have before the string breaks? Answer in units of m/s.

    2. Relevant equations
    m(v^2/r) > T

    3. The attempt at a solution

    I tried plugging numbers into the equation v=sq rt(Tr/m), or sq rt((34.6)(.402)/1.31), which is sq rt(~10.61770992) or ~3.26. The assignment said this was wrong (it's online), so I'm not sure where I went wrong.

    My next question is this:


    I'm pretty sure the equation to solve this is mgsin(theta), but I'm not sure what Mg in the picture is. I've tried both (Mg)(g)(sin(theta)) and just Mg(sin(theta)), but neither have been right. So, I'm wondering what exactly Mg is supposed to be? Or if I'm just using the wrong equation for the problem.

    Thanks for the help.
  2. jcsd
  3. Oct 20, 2008 #2


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    Homework Helper

    In 1) the force it breaks at is 34.6kg*(9.8) N. They only gave you mass.

    In 2) Mg is megagram is 1000kg
  4. Oct 20, 2008 #3
    Correct on both accounts, thank you very much. :)
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