A carnival ride is designed to allow the general public to experience high-acceleration motion. the ride rotates about point O in a horizontal circle such that the rider has a speed v_o. The rider reclines on a platform A which rides on rollers such that friction is negligible. A mechanical stop prevents the platform from rolling down the incline. Determine (a) the speed v_o at which the platform A begins to roll upward (b) the normal force experienced by an 80kg rider at this speed.