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Homework Help: Thermodynamics: Am i correct?

  1. Jan 31, 2016 #1
    1. The problem statement, all variables and given/known data
    In an experiment, 1.1kg of aluminium is heated to 92 degrees Celsius it is then dropped into 0.5kg of water at 12 degrees celsius.

    Find the final temperature of the mixture. (Cw= 4200JKg-1Celsius-1) (Cal= 880JKg-1Celsius-1)

    2. Relevant equations
    Qal = Qw

    3. The attempt at a solution
    (1.1)(880)(92-t) = (0.5)(4200)(t-12)
    968( 92 - t ) = 2100( t - 12 )
    89056-968t = 2100t - 25200
    63856 = 3068t
    20.81 = t
  2. jcsd
  3. Jan 31, 2016 #2

    As you suspected, I suppose.

    You can check your answers yourself: if you put back "t=20.81" in the first line of your equation, you will see that you are way off.
    From your second line, one can see that cooling and heating have a ratio of about 2:1 in temperature.
    Last edited: Jan 31, 2016
  4. Jan 31, 2016 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Your problem lies in the arithmetic used to get the line immediately above.

    Always check your work for arithmetic mistakes.
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