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Homework Help: Find the rate at which its temperature changes

  1. Feb 2, 2005 #1
    ive been working on this problem and i have a solution too, but it doenst work. the reason i know that it doesnt work is because we have to submit our answers to a computer system that tells us if our answer is right or wrong. please help?

    A blackened, solid copper sphere of radius 5.70 cm hangs in a vacuum in an enclosure whose walls have a temperature of 21.0°C. If the sphere is initially at 0.0°C, find the rate at which its temperature changes, assuming that heat is transferred by radiation only. Also assume that the sphere has an emissivity of 1.

    here is what i did:

    Pnet = dQ/dt = mc dT/dt

    one two skip a few and...

    dT/dt = [3eσ(T^4 – T0^4)]/rρc

    its right...but it doenst work!

    please help?
  2. jcsd
  3. Feb 2, 2005 #2
    never mind...i got it...
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