Explain the following:

A ship submerges more as it sails from sea water to river water.

Three different shapes of the same mass are cut from a sheet of iron as shown in the figure given below. Identify the shape with the highest density. Give reason.

The dimensions of a hall are 10 m x 7 m x 5 m. If the density of air is 1.11 kg m^-3, find the mass of air in the hall.

The density of aluminium is 2.7 g cm^-3. Express it in kg m^-3.