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Find d with m and v

  1. May 18, 2008 #1
    If a 50 000 kg locomotive is travelling at 10m/s and its brakes and engine both fail, how far will it roll before coming to a stop.

    Now I know how to do this problem if friction was given but I really dont know which formulas i can combine.

    I think I need to find deceleration but I dont know how with the information given.

    If someone could give me a hint how to get started it would be appreciated:)
     
  2. jcsd
  3. May 18, 2008 #2

    rock.freak667

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    Are you sure that is all the question gave? Because if you ignore friction, then there must be some other force acting on the train, else by Newton's first law, that train should continue to move in a straight line.
     
  4. May 18, 2008 #3
    sorry man, there is no way to find this..because we need to find the deceleration..which is either
    a. negative acceleration because of engine
    b. negative acceleration because of friction

    we know that it's v=10ms-1, but we don't know a time or accel
     
  5. May 18, 2008 #4
    i know, if there was friction i could use ma=mgUs and find acceleration to sub into a kinematics formula to find d skidding

    the question oly gives what i wrote above
     
  6. May 18, 2008 #5
    my textbook gives the answer as 2550m
     
  7. May 18, 2008 #6
    I think you can assume the engine is running constantly, providing a force to push the train. But the train is not accelerating, it is traveling at 10 m/s. When the engine fails, the resistive force that keeps the train traveling at 10 m/s is the only force remaining, since the brakes also fail.

    Sheldon
     
  8. May 18, 2008 #7

    hage567

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  9. May 18, 2008 #8
    definitely helps thank you hage
    I just wasnt expecting that i would have to look up the coefficient of rolling friction like pingpong did.
     
  10. May 18, 2008 #9

    hage567

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    Yeah, I agree that's a bit strange.
     
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