A motorcyclist in a circus rides his motorcycle within the confines of the hollow sphere. If the coefficient of static friction between the wheels of the motorcycle and the sphere is μ_s = 0.4, determine the minimum speed at which he must travel if he is to ride along the wall when θ = 90°. The mass of the motorcycle and rider is 250 kg, and the radius of curvature to the center of gravity is ρ = 20 m. Neglect the size of the motorcycle for the calculation.