Physics

Any thing that floats will displace its weight in water.. Not everything that sinks, like a brick or a chunk of metal will, but only displace its volume of water...

It is the amount of water that an object displaces that determines whether it will sink or float... for this purpose submarines have balast tanks which will have the air drawn out to allow them to submerge, or have air pumped in to them to allow the vessel to float... I think you should get the third question without help...

thank you!