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Homework Help: Simple rolling friciton problem, where did I go wrong?

  1. Oct 18, 2007 #1
    Word for word:

    A50,000kg locomotive is traveling at 10 m/s when its engine and breaks fail. How far will the locomotive roll before it comes to a stop?

    Rolling friction for rubber on concrete is 0.02 (by the book)

    a= fnet/m = (umg)/m so mass cancels out leaving a = ug = .02(-9.8) = -.196

    I use Vf^2 = Vi^2 + 2ad (I'll just say d = distance in meters)
    So it works out to
    -100 = (-0.392)d
    d = 255 m

    but wait... the book says the answer's 2550!

    I would figure that means the rolling friction is .002 but that's steel on steel (dry)

    What am I doing wrong???
     
  2. jcsd
  3. Oct 18, 2007 #2

    TMM

    User Avatar

    I'd assume you need the steel on steel coefficient. Don't locomotives with steel wheels run on steel tracks?

    I don't see why you're using rubber and concrete.
     
  4. Oct 18, 2007 #3
    wow......

    I read that and thought because it's a locomotive, then blood drained from my face.

    a locomotive, a train........ why the hell am I a physics major? lol

    thanks! that's all I needed
     
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