# Some very hot rocks have a temperature of #540 ^o C# and a specific heat of #240 J/(Kg*K)#. The rocks are bathed in #45 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

#### Explanation:

We know that in such interactions heat is gained by one and heat is lost is by the other.

Also that the heat gained/lost is given by

where

In the given problem heat is lost by rocks and gained by boiling water which vaporizes.

Heat gained by boiling water to change into vapours at the same temperature *i.e.*,

Latent heat of vaporization of water is

Now heat lost by rocks to cool down from

Equating (1) and (2) and solving for the required quantity