A piece of copper having an internal cavity weights 264 g in air and 225 g in water. The volume of cavity ( in cm3 )is  (density of  copper=8.8 g cm−3)

Let V1  be the volume of cavity and V2  be the volume of copper material ( excluding cavity)V2=2648.8=30cm3 Loss of weight =Buoyancy force39g=(v1+v2)ρw×gv1+v2=39cm3⇒v1=9cm3