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Specific heat

  1. Aug 23, 2010 #1
    1. The problem statement, all variables and given/known data
    A cup of water put in a freezer (freezer temperature -20 degrees) how long will it take to reach 15 degrees given that its initial temperature is 30. its mass is 300g and its surface area is 0.03m2. the water specific heat is 1.2 J/g °C..

    Assume that the heat transfer occurs only to the air around the cup.. and the overall heat coefficient is 13 KJ/hr m2 °C


    2. Relevant equations
    q = mc(T)


    3. The attempt at a solution
    q = mc(Tf - Ti)
    300*1.2*15
    q = -5400j

    so that’s how much energy is required to cool the cup. which is 5.400 Kj
    but given 13 KJ/hr m2 °C .. but when do i use the freezer temperature??
    im a bit stuck at this point..

    any help would be appreciated thanks.
     
    Last edited: Aug 23, 2010
  2. jcsd
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