Question

a plastic cube is released in water will it sink or come on the surface of water

Answer 1

If a plastic cube is released in water, it will float on the surface due the force of buoyancy.

Although a few types of plastic will sink in water as their specific gravity is greater than water.

But with the assumptions taken, we take the specific gravity of plastic to be less than 1 and thus it will float.

Answer 2

Solution :-

It all depends on which plastic material is used to make the cube. If it is made from some polyolefin plastics such as LDPE, HDPE, LLDPE or PP then it will float on water as these materials has specific density less than 1. But most of the other plastic materials such as ABS, Polyester, Nylon, PVC/Vinyl will sink because they are heavier than water.

Most commercial plastics are not the pure compound but have other materials incorporated including fillers and they are heavier than water. In this condition if the cube is made up of these things then the cube will definitely sink.