Physics problem---At what rate must the cylindrical spaceship rotate if occupants are to experience simulated?

The centripetal acceleration of the occupant is a = v² / r = 0.50 g. We solve for v and obtain v = √(0.50 g x r) = √(0.50 x 9.8 m/s² x 20 m) = 9.9 m/s. The speed of the occupant v = 2πr / to, where to is the time of one revolution. We solve for to = 2πr / v = 2π x 20 m / 9.9 m/s = 13 s