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Homework Help: TEST tomorrow in physics and need help on this problem

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data

    A light-rail train going from one station to the next on a straight section of track accelerates from rest at 1.4 { m/s^2} for 15 { s}. It then proceeds at constant speed for 1100 { m} before slowing down at 2.2 { m/s^2} until it stops at the station.

    What is the distance between the stations?

    How much time does it take the train to go between the stations?

    2. Relevant equations
    (vx)f= (vx)i + ax[tex]\Delta[/tex]t
    xf= xi + (vx)i[tex]\Deltat[/tex] + 1/2ax([tex]\Deltat[/tex])2

    (vx)f2= (vx)i2+2ax[tex]\Deltax[/tex]
    3. The attempt at a solution

    I already know the answer but I cant figure out how to get to the right answer....
    d= 1400m
    t=77s
     
  2. jcsd
  3. Sep 11, 2008 #2
    Split the question into three different parts. Use equations Vf = Vo + at, x= 1/2(Vf + Vo)t.

    For the first part, you are given Vo, a, t. You need to first find Vf, then x.

    For the second part, you are given x and constant v. You must find t. Think about the units.

    For the third part, you are given a (remember, it's deccelerating so it's - ), Vo, and Vf. Find t, then x.

    At the end, add up all the times from the 3 parts to get 77s. And add the displacements together to get 1400m (I got 1357.5m, but 1400m is correct for the number of sig figs).

    I hoped that helped, and that it wasn't too much information on how to solve the question.
     
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