An iron casting containing a number of cavities weight 6000 N in air and 4000 N in water. What is the volume of the cavities in the casting ? Density of iron is 7.87 g/cm3. Take g = 9.8 m/s2 and density of water = 103 kg/m3.
Let v be the volume of cavities and V the volume of solid iron. Then,
