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Math Help - Final velocity?

  1. #1
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    Final velocity?

    Here is the problem:

    A bicyclist starts a timed race at 6.0 mi/h. In order to win, he must average 21 mi/h. Assuming constant acceleration from the start, how fast must he be traveling at the end of the race?

    The answer is 36 mi/h, not 48 mi/h as I answered. Is there a graphical method to this one or am I missing a direct formula method?

    Please help and thanks,

    B
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  2. #2
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    Answer:

    Draw a sloped line segment on a v vs t graph with y-intercept of 6. At the middle of the line is 21. Symmetrically then, the value of y at the end of the line segment is 36. Thus the answer.
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  3. #3
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    Oct 2008
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    Well the easiest way would be to Vaverage=(Vstart+Vend)/2 ..
    Which is logical to you I hope.
    Then you could simply
    Vaverage=(Vstart+Vend)/2 *2
    2Vave=Vs+Ve
    Ve=2Vave-Vs
    Ve=42-6=36

    And yes, graphically, the average should be achieved exactly in the middle of the racing time.
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