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    Here is the paper and the mark scheme:

    http://www.edexcel.com/migrationdocu...e_20090129.pdf

    http://www.edexcel.com/migrationdocu...s_20090312.pdf

    Why does the mark scheme use an integral of y squared? According to the M3 textbook, for x, you use integral of xy,dx divided by integral of y, but the mark scheme uses y squared.

    thanks for any help.
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    (Original post by IL9)
    Here is the paper and the mark scheme:

    http://www.edexcel.com/migrationdocu...e_20090129.pdf

    http://www.edexcel.com/migrationdocu...s_20090312.pdf

    Why does the mark scheme use an integral of y squared? According to the M3 textbook, for x, you use integral of xy,dx divided by integral of y, but the mark scheme uses y squared.

    thanks for any help.
    I think you might be confusing working out the moment of a flat surface with that of a solid.

    The volume of an elementary vertical slice is "pi y^2 dx", so we have the integral of "pi x y^2 dx" for the moment.

    They've left out the pi - presumably because it cancels laters with the denominator.
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    Ah correct, I was mixing up centre of mass of a lamina with that of a volume. Thanks for the help.
 
 
 
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