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Conduction between a steel/copper cylinder.

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data


    A steel cylinder of radius 7.0 cm and length 4.0 cm is placed in end-to-end thermal contact with a copper cylinder of the same dimensions. If the free ends of the two cylinders are maintained at constant temperatures of 85°C (steel) and 20°C (copper), how much heat will flow through the cylinders in 19 min?

    2. Relevant equations

    Q = (kAtdeltaT)/L

    Q=heat
    k for steel=66.9
    k for copper=395
    A=area
    t=time
    T=temperature
    L=length

    3. The attempt at a solution

    x=temperature in the middle of the cylinders

    I set heat transferred through the steel part of the cylinder equal to the heat transferred through the copper part of the cylinder.

    (66.9)(85-x) = (395)(x-20)
    x=29.4

    then using that value, i solved for Q.

    Q=((66.9)(.0154)(85-29.4)(1140))/.04
    so Q=1.6E6 J

    BUT the answer is Q=1.17E6 J
    where'd i go wrong?
     
  2. jcsd
  3. Dec 5, 2009 #2

    ideasrule

    User Avatar
    Homework Helper

    Q=1.17E6 J should be right. Perhaps the answer key is wrong?
     
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