Air flows past a golf ball of 20 mm radius. It is observed that the boundary layer becomes turbulent at Reynolds number of 2 × 105. If the kinematic viscosity of air is 1.5 × 10-5 m2/s, then the speed of air when the flow becomes turbulent is
1
150 m/s
2
90 m/s
3
75 m/s
4
62.5 m/s