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Homework Help: Constant Acceleration of jogging Problem

  1. Jan 29, 2012 #1
    1. The problem statement, all variables and given/known data

    Al and Bert are jogging side by side on a trail in the woods at a speed of 0.75 m/s. Suddenly, Al sees the end of the trail 35 m ahead and decides to speed up to reach it. He accelerates at constant rate of 50 m/(s^2) while Bert continues on at a constant speed. (a) How long does it take Al to reach the end of the hill?

    Part (a) is the one I'm having trouble understanding.

    2. Relevant equations

    Δx = (1/2)at^2 + Vt + X

    3. The attempt at a solution

    35 = (1/2)(0.50)t^2 + (0.75)t
    35 = (0.25)t^2 + (0.75)t
    35 = t[(0.25)t + 0.75]
    35/t = (0.25)t + 0.75

    And, that is where I stopped. I'm sure I pretty much went wrong at the third step.
  2. jcsd
  3. Jan 29, 2012 #2


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    Homework Helper

    Your summation is correct.

    To solve a quadratic equation, you re-arrange to make the rhs zero, then solve by either factorisation [if you are lucky] or use the quadratic formula.
  4. Jan 29, 2012 #3
    Are you sure of the question wording?.....you have an acceleration of 50m/s^2
    Which is not realistic.
    In your calculation you have 0.5 which is more realistic
  5. Jan 29, 2012 #4
    Holy crap, I forgot about the quadratic formula. :surprised Thanks for the help.
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