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Math Help - Word Problem

  1. #1
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    Word Problem

    A projectile is shot upwards with an initial velocity of 30m/s. Its height at time t is given by h=30t-4.9t^2. During what period of time is the projectile more than 40m above the ground? Express your answer rounded to the nearest hundredths.
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  2. #2
    Member integral's Avatar
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    40=30t-4.9t^2
    Use the quadratic formula.

    t=\frac{-30+\sqrt{900-784}}{2(-4.9}
    <br />
t=\frac{2\sqrt{29}-30}{-9.8}

    t=\frac{150\pm10\sqrt{29}}{49}

    t_1=4.16
    t_2=1.96
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