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Homework Help: Acceleration Question* * (Physics 11)

  1. Oct 30, 2007 #1
    Acceleration Question*URGENT* (Physics 11)

    Okay well i have a test tomorrow and this is a question that was on my quiz, and i didnt know how to do this:

    1. The problem statement, all variables and given/known data
    1. A driver of a car going 90.0km/h suddenly sees a barrier 40.0m ahead. It takes the driver 0.75s before she applies the brakes, and the average acceleration during braking is -10.0m/s^2.
    a. determine if the car hits the barrier (need to know how you got it, please tell me which equation and why :/ i know this involves 2 steps.)
    b. what is the maximum speed at which the car could be moving and not hit the barrier 40.0m ahead? assume acceleration doesnt change.


    2. Relevant equations



    3. The attempt at a solution
    I haven't a clue, need help >.<
     
  2. jcsd
  3. Oct 30, 2007 #2

    andrevdh

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    Homework Helper

    During the 0.75 seconds the driver is moving with a constant speed. Use the speed and time to calculate the distance covered in this time interval. The distance to the barrier is now reduced by this amount. That is

    [tex]d_{remain} = 40.0 - d_{react}[/tex]
     
  4. Oct 30, 2007 #3
    and then, apply the equation of motion (s-u-v-a-t equations) to check what distance it takes to stop. (you know u, v, and a.)
    Drawing a rough sketch always helps in Physics. Even in such a simple question.
     
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