(a) Let us consider a cylindrical section at a distance of r and having thickness dr.

The volume of fluid flowing from this section per second

So, the volume of fluid flowing across the section of the tube in unit time

(b) The kinetic energy of the fluid within the volume element of thickness dr

So, the K.E. of fluid within the tube

Integrating, we get

(c) The viscous drag exerts a force on the tube

(d) The pressure difference ΔP is given by

ΔP = P_{2} – P_{1} = P

Where P_{1 }= 0 & P_{2} = P

As we know that

P = Force (F)/ area of section of tube