Asmall button placed on a horizontal rotating platform with diameter 0.520 m will revolve with the platform when it is brought up to a speed of 40.0 rev> min, provided the button is no more than 0.220 m from the axis. (a) what is the coefficient of static friction between the button and the platform? (b) how far from the axis can the button be placed, without slipping, if the platform rotates at 60.0 rev> min?