A submarine has a mass of 2.0×106kg (including the air trapped within it) and an airtight hull that encloses a volume of 2000m3. The submarine is initially floating in sea water of density 1030kgm−3. Sea water can be pumped into special ballast tanks to change the overall density of the vessel.
(i) Show by calculation whether the submarine will float or sink in its initial condition.
(ii) Calculate the minimum mass of sea water that must be taken into the ballast tanks so that the submarine is just on the point of sinking.
(iii) After submerging, explain qualitatively how the submarine’s crew can make it rise again to the surface using the same principle.