A calorimeter of mass 50 gm and specific heat capacity 0.42 J `g^-1 ^@C^-1` contains some water at `20^@`C.
A metal piece of mass 20 gm at `100^@`C is dropped into the calorimeter. After stirring, the final temperature of the mixture is found to be `22^@C`.Find the mass of water used.
(specific heat of metal piece=`0.3 J g^-1 ^@C^-1` specific heat of water =`4.2 J g^-1 ^@C^-1`)