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Conservation of linear momentum

  1. Oct 30, 2012 #1
    1. The problem statement, all variables and given/known data
    A runaway 14,000 kg railroad car is rolling horizontally at 4.00 m/s toward a switchyard. As it passes by a grain elevator, 2000 of grain suddenly drops into the car. Suppose the there is a small vertical chute in the bottom of the car so that the grain leaks out at 10 kg/s. How long does it take the car to cover 500m


    2. Relevant equations
    Pi = Pf



    3. The attempt at a solution
    Picture attached
     

    Attached Files:

  2. jcsd
  3. Oct 30, 2012 #2

    Andrew Mason

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    What is the initial horizontal momentum of the car and how does that relate to the horizontal momentum of the car + grain after the grain drops? Can you determine the speed of the car + grain after the drop? What effect does the vertical leak of grain have on the horizontal speed of the car?

    AM
     
  4. Nov 2, 2012 #3
    I already included those in my paper (attached).
    However I can't determine the speed of the car + grain after drop unless I know the time.
     
  5. Nov 3, 2012 #4

    Andrew Mason

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    Sure you can. How does the horizontal momentum before the collision compare to the horizontal momentum after the collision? (hint: are there any forces acting in the horizontal direction that are external to the car - grain system?).

    AM
     
  6. Nov 3, 2012 #5

    haruspex

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    Andrew is asking what the speed is immediately after the drop, i.e. t = 0.
    Separately, he asks what affect the grain leak has on the car thereafter.
     
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