A viscous liquid fills the annular gap between vertical concentric cylinders. The inner cylinder is stationary with a radius of R1 and the outer cylinder rotates at a constant velocity of ωR2. The flow is laminar. The velocity of the fluid in the z, r, and θ direction are: When R1 = 0.9R2, R2 = 0.1m, ω = 10 radians/s and viscosity of the fluid is 0.001Pa·s. Calculate the shear stress at the surface of the inner cylinder. Answer should have the unit of Pa.