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Homework Help: Easy heat transfer problem stuck

  1. Jun 19, 2006 #1
    An open container holds 0.550 kg of ice at -15 Celsius. The mass of the container can be ignored. Heat is supplied to the container at the constant rate of 800 J/min for 500 min.

    A) After how many minutes does the ice start to melt.
    This part I calculated and got correct, it's 21.7 min.,

    B) After how many minutes, from the time when the heating is first started, does the temperature begin to rise above 0 Celsius?
    This is where I'm stuck. What I did was say that Qtotal would be equal to Q1 (the heat necessary in part A) + Heat of Fusion of water * the mass of the ice.
    so: Qt = Q1 + Lm
    L is 335,000 J/kg
    m is 0.550 kg
    Q1 from part A is 17325 J.

    So, Qt = 35750 J

    Time is Qt/rate of transfer = 35750 / 800 = 44.7 min, but that's incorrect...

    What am I messing up?

  2. jcsd
  3. Jun 19, 2006 #2


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    Staff Emeritus
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    You may wish to check this value.
  4. Jun 19, 2006 #3
    Yeah, I used the wrong value for the heat capacity of ice. (Used 33400 instead of 334000).
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