Question

a plastic cube is released in water.will it sink or come to the surface of water?

Answer 1

the density of plastics is less than that of water so it will float on the surface

Answer 2

It seems like they ought to sink because we're used to seeing things fall. But for the ship to sink it has to push aside some water, which has nowhere to go but up. So it's a question: does the ship 'want' to sink more than the water 'wants' not to rise? It turns out that just depends on whether the ship weighs more or less than the amount of water that would fill the same space. Real ships have lots of air inside, so they weigh less than the same volume of water, so they float.