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Homework Help: Kinematics problem help

  1. Nov 8, 2007 #1
    Q: The average alcohol-free driver requires about 0.8 s to apply the brakes
    after seeing an emergency. Calculate the distance travelled after seeing the emergency
    before applying the brakes.

    with the question, the given speed is 17 m/s and t = 0.8.
    at first, i used d =vt equation to find the distance, however,
    when i read through the question again, i had a feeling that it's not right.
    my first answer was d=14m, but it just doesnt look correct.

    i was thinking of finding the acceleration then use v[tex]^{2}_{f}[/tex]=v[tex]^{2}_{i}[/tex] +2a[tex]\Delta[/tex]d
    to solve for d, OR, use this equation, [tex]\Delta[/tex]d=1/2(v[tex]_{1}[/tex]+v[tex]_{2}[/tex])[tex]\Delta[/tex]t, without
    even having to find the acceleration.

    one part of my knowledge tells me that i don't need acceleration to do this question
    because this is about "before" applying the break.

    its confusing me..

    any help would be greatly appreciated.

    thank you
    Last edited: Nov 8, 2007
  2. jcsd
  3. Nov 8, 2007 #2


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    Science Advisor
    Homework Helper

    You "know" what you did is right. Resist the temptation to complicate it. I'm sure you'll get a chance to use that other stuff later.
  4. Nov 8, 2007 #3

    If Dick's reply isn't enough, your logic is right to me, simple enough. I don't see how it doesn't "look correct".
  5. Nov 8, 2007 #4
    Thank you, I really appreciate it! :)
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