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Homework Help: Velocity/acceleration/time to stop

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data

    The brakes on your car are capable of slowing down your car at a rate of 4.9 m/s^2.
    If you are going 132 km/h and suddenly see a state trooper, what is the minimum time in which you can get your car under the 90 km/h speed limit?

    2. Relevant equations

    v(t)= at + initial velocity

    (final velocity^2) - (initial velocity^2) = 2*a*delta X (change in position)

    3. The attempt at a solution

    I came out with 8.57 seconds. Is there some converting I maybe missed?
     
  2. jcsd
  3. Feb 5, 2009 #2

    Delphi51

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    Homework Helper

    Hi Laurie, welcome to PF!
    I don't know how you got 8.57. I got between 2 and 3s. Show your calc and we'll find your error.
    Did you remember to convert the speeds to m/s ?
     
  4. Feb 5, 2009 #3

    No, I didn't convert. Whoops. So let me work this out again. Thanks for the advice.
     
  5. Feb 5, 2009 #4
    2.380952388 seconds. :!!) Thanks soooo much for your help!!
     
  6. Feb 5, 2009 #5

    Delphi51

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    Homework Helper

    Most welcome!
     
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