A disc of radius r = 20 cm is rotating about its axis with an angular speed of 20 rads-1. It is gently placed on a horizontal surface which is perfectly frictionless. What is the linear speed of any point on the periphery of the disc? (in m/s)
Since the surface is perfectly frictionless, the disc will not roll on the surface, it will simply keep on rotating at the place where it is placed.
Now
Linear speed = distance from centre X angular speed
Given, r = 20 cm = 0.2 m and = 20 rad s-1.
Linear speed of point on the periphery = r = 0.2 x 20 = 4 ms-1.