One of the unique properties of water is that when it is in the solid state, it's density actually decreases(which is very different from other substances in the known universe). WHY do u think this is important?

A lost shipping container is found resting on the ocean floor and completely submerged. The container is 6.3 m long, 2.9 m wide, and 2.9 m high. Salvage experts attach a spherical balloon to the top of the container and inflate it with air pumped down from the surface. When the balloon's radius is 1.6 m, the shipping container just begins to rise towards the surface. What is the mass of the container? Ignore the mass of the balloon and the air within it. Do not neglect the buoyant force exerted on the shipping container by the water. The density of seawater is 1025 kg/m³. Number i Units

it’s a lovely day and you decide to launch a giant helium balloon. Once filled, your balloon is a perfect sphere with a radius of 6.90 m. You consider having the balloon lift a crate of water balloons. What is the maximum weight the filled helium balloon can just lift (solve for the equilibrium condition where upward force equals downward force)? Assume that the membrane of the helium balloon has a mass of 920 kg (this does not include the mass of the helium within nor the mass of the crate). Neglect the buoyant force on the crate of water balloons. Density of He is 0.179 kg/m3. Density of air is 1.29 kg/m3. Volume of a sphere is 4/3 π r3. Weight is in N (not kg)

A cube of some unknown substance is held submerged in water. The cube has a mass of 0.540 kg and a volume of 0.000770 .What is the acceleration of the cube when it is released?