A corn placed on a rotating turntable just slips if it is placed at a distance of 4 cm from the center. If the angular velocity of the
turntable is doubled, it will just slip at a distance of
The friction force required to keep it rotating is equal to 
. Now at 4cm away from the center when it just slips, the
static frictional force is at its limiting value. If the angular speed of the turntable is doubled the magnitude of the required centripetal
force increases 4 times. So, to keep it within the limiting value of frictional force the radius of turntable must be made 1/4 of initial
radius. 
= 
2