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Math Help - mass of disc

  1. #1
    Oct 2007

    mass of disc

    A disk of radius 5 cm has density of 10 gm/cm^3 at its center, density of 0 at its edge and the function of its density is linear function of the distance from the center. Find the mass of the disk.

    Would my function be (10 - r) r dr dtheta?

    I am going from 0 to 2pi and from -5 to 5 Is this correct?

    THanks again for all the help this site's members have given to me. Frostking
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  2. #2
    MHF Contributor Calculus26's Avatar
    Mar 2009
    The integrand is correct

    However, the limits for r are 0 to 5.

    To sweep out the disk r varies from the origin to the edge and then as theta varies from o to 2pi the entire disk is swept out.

    A technical point
    since you are regartding the thickness as negligible the density
    shoud be 10gm/cm^2 otherwise you final result would be in gms/cm obviously not what you want
    Last edited by Calculus26; May 26th 2009 at 02:53 PM.
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