When water at 20C ( = 998 kg/m3, = 0.001 kg/ms) flows through an 8-cmdiameter pipe, the wall shear stress is 72 Pa. What is

When water at 20°C (ρ = 998 kg/m3, μ = 0.001 kg/m⋅s) flows through an 8-cmdiameter pipe, the wall shear stress is 72 Pa. What is the axial pressure gradient (∂ p/∂ x) if the pipe is (a) horizontal; and (b) vertical with the flow up?