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String break physics problem

  1. Oct 1, 2009 #1
    A 630 gram rock is whirled on the end of a string 49 cm long which will break under a tension of 20 N.

    a) What is the highest speed the rock can reach before the string breaks? (Neglect gravity.)
    V=M/S

    T- mg= ma

    T-mg= m(v^2/r) solve for v

    i get 2.188 m/s (which is wrong)

    20-(630*9.8)= (630)(v^2/.49)

    I converted 49 cm into .49 meters

    help?
     
  2. jcsd
  3. Oct 1, 2009 #2
    Re: tension

    I don't know why you have the mg term in there. I think all you need is the T=mv^2/r and solve for v.
     
  4. Oct 1, 2009 #3
    Re: tension

    20= (630)*( (v^2)/ .49)

    v= .125 m/s... that was wrong when i plugged it in
     
  5. Oct 1, 2009 #4
    Re: tension

    nvm, i got it. conversion problem thanks!
     
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