Consider a 20 kg uniform circular disk of radius 0.2 m. It is pin supported at its center and is at rest initially. The disk is acted upon by a constant force F=20 N through a mass less string wrapped around its periphery as shown in the figure.

Suppose the disk makes n number of revolutions to attain an angular speed of $50rad{s}^{-1}.$ The value of n, to the nearest integer, is……………. [Given : In one complete revolution, the disk rotates by 6.28 rad]