The average velocity in the pipe is

Question

The oil with specific gravity 0.8, dynamic viscosity of $8\times 10^{-3}Ns/m^{2}$ flows through a smooth pipe of 100 mm diameter and with Reynolds number 2100.  The average velocity in the pipe is

(a) 0.21 m/s                    (b) 0.42 m/s

(c) 0.168 m/s               (d) 0.105 m/s