Question

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

Answer 1

Consider that, you have the purest form of water and its specific gravity is 1. After that, it is necessary to find what type of plastic your cube is made up of.

If the plastic is lesser than 1 then it will float otherwise it will sink. Other than that, additives added to the plastic will push up the specific gravity either above or below to make the plastic to sink or float.

Answer 2

If a plastic is released in water then :

a. It will float if it's density is less than the density of water.
b. It will sink if it's density is much more than the density of water.

The boynd force Plays a major role in floating an object on its surface.