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Train problem

  1. Jun 29, 2009 #1
    Hey I was hoping some would be able to help me or show me how to calculate the amount of force a train exerts on a spot on a track.

    Simply I could calculate the force exerted on a spot of the track as the weight of the train in kgs times the gravity (9.8m/s^2) will give me netwons of force.

    But... I want to know if trains are moving and also can I assume the whole weight of the train exerts on that point??

    thanks for any help
     
  2. jcsd
  3. Jun 29, 2009 #2

    russ_watters

    User Avatar

    Staff: Mentor

    You'll just need to divide by the number of wheels.
     
  4. Jun 29, 2009 #3
    You need the weight of the train (its mass times g) divided by the total area that is making contact with the ground.
     
  5. Jun 29, 2009 #4
    ok, what about the moving portion or velocity of the train, will that alter the amount of force exterted down on the spot?

    Ok by dividing by the number of wheels I can assume that fraction of the trains weight ( that amount of weight per wheel )is focused on that small spot?

    Thanks guys for the help
     
  6. Jun 29, 2009 #5
    well you can find the weight that each wheel must support, however that assumes a homogenous train. The velocity of the train would have no effect. It is directed in a direction perpindicular to gravity (assuming the train is on a flat track)
     
  7. Jun 29, 2009 #6
    I think a freight car weighs about 130 tonnes (tonne-wt)= 1.275 x 10^6 Newtons (engines are heavier). This weight is supported by eight steel wheels, so the weight per wheel is about 1.59 x 10^5 Newtons. There are about 100 cars in a typical freight train, so there are about 400 wheels, each with this weight, rolling over every piece of track every time a freight train goes by. Suppose the total area under each wheel supporting the load is 10 cm^2 (guess). Then the compression pressure (stress) is 1.59 x 10^5 Newtons/.001 meters^2 = 159 megaPascals (MPa). This about the allowable compressive stress limit for steel.
     
    Last edited: Jun 30, 2009
  8. Jun 29, 2009 #7
    cool thanks
     
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