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Math Help - Physics Kinematics Equation Must Be Solved W/ Algebra

  1. #1
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    Physics Kinematics Equation Must Be Solved W/ Algebra

    So I have the formula and values substituted in correctly - but now the simple algebra part is killing me.
    x = vt + 1/2at^2
    .06=(2*10^3)t + 1/2(4*10^7)t^2

    What is t?
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  2. #2
    Senior Member eumyang's Avatar
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    .06 = (2*10^3)t + 1/2(4*10^7)t^2
    .06 = 2000t + 20000000t^2

    Set equal to 0 and rearrange:
    20000000t^2 + 2000t - 0.06 = 0

    Use the quadratic formula:
    \begin{aligned}<br />
t &= \dfrac{-2000 \pm \sqrt{2000^2 - 4(20000000)(-0.06)}}{2(20000000)} \\<br />
&= \dfrac{-2000 \pm \sqrt{4000000 + 4800000}}{40000000} \\<br />
&= \dfrac{-2000 \pm \sqrt{8800000}}{40000000} \\<br />
&\approx 2.42 \times 10^{-5}, -1.24 \times 10^{-4}<br />
\end{aligned}
    Last edited by eumyang; August 9th 2010 at 07:12 PM. Reason: Fixed typos.
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  3. #3
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    Yikes! You should have studied Quadratic Equations over the previous years.

    If you write it like this: Żat^2 + vt - x = 0, you should find solutions from the Quadratic Equation, or Completing the Square. Ringing any bells, yet?
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