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Homework Help: Will the car hit the barrier?

  1. Feb 24, 2007 #1
    Hi there, I am a grade 11 student, learning physics.

    1. The problem statement, all variables and given/known data

    A driver of a car going 90km/h suddenly sees the lights of a barrier 40.0 m ahead. It takes the driver 0.75s before he applies the brakes and the average accelleration during braking is -10.0m/s2.
    a) Determine whether or not the car hits tha barrier.
    b) What is the maximim speed at which the car could be moving and not hit the barrier at 40.0 m ahead? Assume the accelleration does not change.

    a) Treat toward the barrier as positive.
    v2=0m/s delta(t)= 40

    I am not quite sure how to do b)

    2. Relevant equations

    v2^2 = v1^2 + 2a(delta(d)) <---- a)

    3. The attempt at a solution

    I have already determined that it would take the car 50 m to come to a complete stop, so it would hit the barrier.

    I am having trouble with b)

    thanks in advance.
  2. jcsd
  3. Feb 24, 2007 #2
    I could be wrong but you just need to use the same formula again:

    v2^2 = v1^2 + 2a(delta(d)) <---- a)

    You know d, v2 is 0, and your given acceleration from before

    There is only one unknown left, V1.
  4. Feb 24, 2007 #3


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    Homework Helper

    If you assume the car will stop just before it hits the barrier, you now have a new piece of information you can use in your equations to work out the new v1.
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