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Homework Help: How many grams of cold water necessary to lower temperature in container

  1. Sep 22, 2009 #1
    1. The problem statement, all variables and given/known data
    How many grams of 20 degree C water do I need to add to 100 grams of 80 degree C of water to get the final temperature down to 50 degrees C?

    2. Relevant equations
    I'm sure it's a pretty simple equation, but I don't know it. (I'm studying a lot of different things at once and am not in school)

    3. The attempt at a solution
    Not sure.

    Thanks :)
  2. jcsd
  3. Sep 22, 2009 #2
    First you need to know the equation for energy, which is q=c*m*deltaT, where deltaT is T(final)-T(initial). You also know that q of the 20 degree water equals the negative of the 80 degree water. Given this, you should be able to solve for grams of 20 degree water.
  4. Sep 22, 2009 #3
    q is heat energy, correct? Why is one the negative of the other?
  5. Sep 23, 2009 #4
    One is negative of the other because the heat that leaves the 80 degree water is added to the 20 degree water.
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