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Homework Help: Acceleration of a Train Problem

  1. Sep 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A train slows down as it rounds a sharp horizontal turn, slowing from
    90.0 km/h to 50.0km/h in that 15.0s that it takes to round the bend. The
    radius of the curve is 150m. Compute the acceleration at the moment the train
    speed reaches 50.0 km/h. Assume that it continues to slow down at this time at
    the same rate.


    2. Relevant equations



    3. The attempt at a solution
    Find the radial and tangential accelerations then get total acceleration. Direction
    will be tan-1 of those. I've tried to start but my numbers don't seem to be
    right. I've drawn a sketch.
    Thanks,
    Kevin
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 17, 2008 #2
    Please do post what you have calculated. What you say seems perfectly right to me.
     
  4. Sep 17, 2008 #3
    First I find the velocity by taking 50.0km/h - 90.0 km/h / 15s
    I converted the km to 833.3m/s - 1500m/s/15s
    I get velocity to be -44.4m/s
    I used the radial acceleration equation (-44.4m/s)2 / 150m to get 13.14m/s2 inward.
    I'm not sure how to get the tangential from here.
    Thanks,
    Kevin
     
  5. Sep 17, 2008 #4
    You made an error converting from Km/h to m/s
    90 Km/hr= 25 m/s
    50 Km/hr=13.8889 m/s

    a(tangential)=(25-13.8889)/15
    a(radial)= [tex]v^{2}/r[/tex] where v=13.8889 an r=150
     
  6. Sep 17, 2008 #5
    I'm not sure where my conversion came from
    I get a tan acc to be .74 m/s2
    I get a radial acc to be 1.2860 m/s2

    I get 1.48 m/s2 inward acceleration by squaring the acceleration and then
    getting the square root.

    For angle is the tan/radial or is the radial/tan to figure angle?

    Thanks for your help. I'm understanding this alot better.

    Kevin
     
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