A disc of radius r = 20 cm is rotating about its axis with an angular speed of 20 rad s-1. It is gently placed on a horizontal surface which is perfectly frictionless (Fig). What is the linear speed of point A on 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 point B where it is placed. NowLinear speed = distance from centre × angular speedGiven, r=20cm=0.2m and ω=20rads−1∴Linear speed at point A=OA×ω=rω=0.2×20=4 ms-1.