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Homework Help: Car rolling and Friction

  1. Sep 23, 2008 #1
    1. The problem statement, all variables and given/known data

    a. A 49,000 kg locomotive is traveling at 11 m/s when its engine and brakes both fail. How far will the locomotive roll before it comes to a stop?

    b. Determine the stopping distance if the locomotive had the same initial velocity but was "low on diesel" so its mass was only 35,000 kg.

    2. Relevant equations

    Fr = ┬Ár x n
    F = ma
    Max = F1 - F2
    May = F1 - F2

    3. The attempt at a solution

    To start off I drew a force diagram which showed thre forces; normal force going up, weight going down, and friction going in the opposite direction of the car. I found weight by multiplying the mass by 9.8, which ended up being 408200. I know that this must also be the amount for the normal force. But, now I'm at a standstill. I don't think the coefficients have anything to do with the problem but I'm starting to second guess myself. Am I able to use the mass and weight to figure out the decceleration of the car so that I will be able to use the velocity to find the distance? Thank you in advance!
  2. jcsd
  3. Sep 23, 2008 #2
    It looks to me like you need the coefficients of friction.
  4. Sep 23, 2008 #3
    That seems logical, but there is no way to get them with just the mass and velocity. Velocity seems pretty pointless, especially at this stage in the problem, and all that mass can give us is weight, but using 9.8 as the acceleration.

    How else can I approach the problem?
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