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Trying to find displacement using velocity and acceleration

  1. Sep 17, 2013 #1
    1. The problem statement, all variables and given/known data
    A train traveling at a velocity of 60.0 m/s is slowed down at a uniform rate of 1.25 m/s2. How far will it travel before its velocity is 1/2 its original value?


    2. Relevant equations
    v2 = vo2 + 2ad


    3. The attempt at a solution
    I first need to isolate my variable, so 'd'. In which case, I believe the equation would then look like 'd=vo2 [itex]\div[/itex] v2+2a. Filling in this equation with the numbers then looks like: d=60m/s2[itex]\div[/itex]30m/s2+2(-1.25m/s2). But when I calculate it all out I'm left with d=-0.5m/s2. This does not make any sense though; it's not possible for the train to travel a negative amount of distance. And also, isn't displacement measured in units of length and not time? I can't figure out how to get rid of the seconds. Needless to say, I am very confused. Thanks in advance.
     
  2. jcsd
  3. Sep 17, 2013 #2

    haruspex

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    I don't. Try that manipulation again. If you're still stuck, post your detailed working.
     
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