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Angular Acceleration problem

  1. Nov 25, 2012 #1
    Hi, thanks for taking a look!

    A toy train rolls around a horizontal 1.4-m-diameter track. The coefficient of rolling friction is 0.12.
    (a) What is the magnitude of the train's angular acceleration after it is released?
    (b) How long does it take the train to stop if it's released with an angular speed of 16 rpm?

    I think I know which equations to use: α = ω^2*r and a = rα, but there is no mention of velocity in the problem so I am stuck.
     
  2. jcsd
  3. Nov 25, 2012 #2

    tiny-tim

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    welcome to pf!

    hi carleon! welcome to pf! :smile:
    find a (from F = ma), then divide by r to get α :wink:
     
  4. Nov 25, 2012 #3
    Re: welcome to pf!

    Thanks, but since mass isn't given, how would I find F=ma?
     
  5. Nov 25, 2012 #4

    tiny-tim

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    call the mass "m" … it'll cancel :smile:
     
  6. Nov 25, 2012 #5
    I got it! α=1.68rad/s^2

    Thanks a bunch. :biggrin:
     
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