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Homework Help: Specific Heat Capacity

  1. May 12, 2009 #1
    Just revising for my practical physics exam tomorrow and got stuck on this!! not sure if its correct, just annpyed me that i was unsure!
    1. The problem statement, all variables and given/known data
    A vending machine for serving hot drinks has a tank of capacity 7.5 litres, and the manufactuurers say that 45 cups of hot water (at 99o C) can be produced at any one time.
    a) what is the volume of one cup
    b) if 170 cups can be produced in one hour, what is the power of the heater? assume that the water starts at a temperature of 20 0 C and that there are no energy losses.
    2. Relevant equations
    Q=mc delta t
    s.h.c of water = 4200 j/kg/k
    3. The attempt at a solution
    a) 7.5/45 = 0.16 litres
    b) 1 litre of water = 1 kg
    7.5 litres = 7.5 kg
    Q=mc delta t= 7.5*4200*79= 2488500 J ( thats for 45 cups)
    so for 170 cups Q= (2488500/45)*170= 9401000 J
    P=E/t= 9401000/3600 = 2611.4 W
    not sure if this is the correct method, any help will be greatly appreciated!!
  2. jcsd
  3. May 12, 2009 #2
    I don't see anything wrong with what you did.
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