(A) Reynold number of fluid flow=500 and its bore diameter=100mm, Density is = 800
The coefficient of viscosity is 0.08 Ns/m2
we know that,
v= 0.5 m/s
Now, for finding velocity at 40 mm dia we use Poiseulli equation for laminar flow
this is the velocity of fluid at radius of 40 mm
(B) External flow is that type of flow which is highly viscous and develop to boundary layers it is due the the characteristic causing interaction between body and fluid.