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Thread: long question, help needed!

  1. #1
    Nov 2008

    long question, help needed!

    This is a long question whilch i think involves the quadratic formula, but i generally dont know where to start with this so any help would be much appreciated.

    "In an engineering test, a rocket sled is propelled into a target. The sledís distance d in meters from the target is given by the formula d = -1.5t^2 + 120 where t is the number of seconds after rocket ignition. How many seconds have passed since rocket ignition when the sled is 10 meters from the target?"
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  2. #2
    MHF Contributor
    skeeter's Avatar
    Jun 2008
    North Texas
    you are given $\displaystyle d = 10$ ...

    $\displaystyle 10 = -1.5t^2 + 120$

    $\displaystyle 1.5t^2 = 110$

    $\displaystyle t^2 = \frac{220}{3}$

    since $\displaystyle t > 0$ ...

    $\displaystyle t = \sqrt{\frac{220}{3}}$
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