Some very hot rocks have a temperature of #240 ^o C# and a specific heat of #140 J/(Kg*K)#. The rocks are bathed in #84 L# of boiling water. If the heat of the rocks completely vaporizes the water, what is the minimum combined mass of the rocks?

1 Answer
Gió
Apr 22, 2016

I found #9685.7kg# although it seems quite a lot (will it fit inside the water?).

Explanation:

I assumed that once reached the boiling point the water is left alone and the rocks are immediately thrown in without any other input of energy from outside.

We can use the relationship of concervation of energy in terms of heat #Q# as:
#Q_("in")+Q_(out)=0#
The rocks cool down giving energy to the water that uses it to vaporize (NOT increase its temperature because already at boiling point):

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