Question

Why is a measured amount of water needed to determine the specific heat of a metal object?

Answer 1

This  is  because  absorbed  heat  energy or  released  by  water  is dependent on  mass of  water.
q=mc delta  T
where  q is  the amount  of  energy  required,   m  is  the  mass , C  is   the  specific  heat  capacity  and  delta  T is change  in  temperature.