The answer for this problem is to use the radial acceleration formula which is:
Radial acceleration = ω^2*R
121000*9.81 m/s^2 = ω^2*0.55 m ω^2 = 121000*9.81/0.55
ω = 1469 rad/s with ω = 2pi*f --> f = ω/(2pi) -->
f = 1469/(2pi) = 234 rps = 234 * 60 rpm
= 14040 rpm
