Question

An iron nail sinks in water, while a ship made of iron floats.

Answer 1

1. The density of iron is more than the density of water therefore the weight of the nail is more than the upthrust experienced by it causing it to sink.
2. However a ship although much larger than the nail floats because the ship is hollow from the inside and this space is filled with air which reduces the average density of the ship lower than that of water.
3. We know that, while floating the weight of the floating body is equal to the weight of the liquid displaced by its immersed part.
4. Thus even with a small portion of the ship submerged underwater, the weight of the water displaced by it becomes equal to the weight of the entire ship.