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

[Paulo Serrano]

Homework Statement

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?

Homework 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)

The Attempt at a Solution

Not sure.

Thanks :)

 

[w3390]

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.

 

[Paulo Serrano]

q is heat energy, correct? Why is one the negative of the other?

 

[w3390]

One is negative of the other because the heat that leaves the 80 degree water is added to the 20 degree water.