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Math Help - Easy (and short) problem

  1. #1
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    Easy (and short) problem

    The amount of bending, B mm, of a particular wooden beam under a load is given by B = 0.2m^2 + 0.5m +2.5, where m kg is the mass (or load) on the end of the beam. What mass will produce a bend of 8.8 mm?

    I tried to substitute 8.8 for B and then subtracted it from both sides of the equation. After this I tried to use the quadratic formula but was unsuccessful.



    Please provide complete working out.
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by Joker37 View Post
    The amount of bending, B mm, of a particular wooden beam under a load is given by B = 0.2m^2 + 0.5m +2.5, where m kg is the mass (or load) on the end of the beam. What mass will produce a bend of 8.8 mm?

    I tried to substitute 8.8 for B and then subtracted it from both sides of the equation. After this I tried to use the quadratic formula but was unsuccessful.



    Please provide complete working out.
    Post your working so we can show you where you went wrong, since you have the correct idea on how to do this problem.
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  3. #3
    Senior Member Stroodle's Avatar
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    The way I'd solve it is:

    88=2m^2+5m+25

    2m^2+5m-63=0

    (2m-9)(x+7)=0

    \therefore m=4.5 kg

    As m can't be negative
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  4. #4
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    Quote Originally Posted by Chris L T521 View Post
    Post your working so we can show you where you went wrong, since you have the correct idea on how to do this problem.
    B = 0.2m^2 + 0.5m + 2.5
    8.8 = 0.2m^2 + 0.5m + 2.5
    0.2m^2 + 0.5m - 6.3 = 0

    Using Quadratic formula = confusing result
    (sorry I can't use LaTex)
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  5. #5
    Senior Member Stroodle's Avatar
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    Worked for me when I used the quadratic formula:


    \frac{-0.5+\sqrt{0.5^2-4(0.2)(-6.3)}}{2(0.2)}=4.5
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