Question

why does a penny sinks in water whereas a ship floats in water?:

Answer 1

Since the ship is designed in such a way that its effective density (m/V) is less than the density of the water.

V = volume of ship

m = mass of ship.

So it floats upon the water. Hence the ship does not sink.

For the penny,

The density of penny (as of iron or silver) is much larger than the water. So it sinks easily.