Question

Why does a block of plastic released under water comes up to the surface of water?

Answer 1

We know that when a body is fully or partially immersed in a liquid a buoyant force will act on it in the upward direction. When it is more than gravity, it will bring it to the surface of water. Buoyancy force is more than gravity for materials with density smaller than water which holds for plastic and hence it comes up to the surface of water.