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Need help on Calculus/Physics problem

  1. Dec 2, 2007 #1
    The temperature in a star of conductivity 1 is inversely proportional to the distance from the center: u=7/(sqrt(x^2+y^2+z^2).
    If the star is a sphere of radius 3, find the rate of heat flow outward across the surface of the star.

    Not sure where to even start.
  2. jcsd
  3. Dec 2, 2007 #2


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    Put the center at (0,0,0). The temp at the center is infinite (can you see why?)

    What is the distance of any point on the surface to the center?
  4. Dec 2, 2007 #3
    I understand that, the distance of any point on the surface to the center is 3 (the radius). But how do I use gauss Law or whatever?
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