Answer : The pressure difference required is, 
Explanation : Given,
Length of tube = 2.0 m
Diameter of tube = 1.0 mm = 1.0 × 10⁻³
Average speed of water = 4.0 m/s
Viscosity of water at 40°C = 0.7 × 10⁻³
The expression used for pressure difference is:

where,
= pressure difference
= viscosity of water = 0.7 × 10⁻³
L = length of tube = 2.0 m
A = area of tube = 
= average speed of water = 4.0 m/s
Now put all the given values in the above expression, we get:


Thus, the pressure difference required is, 