How does pressure energy influence fluid flow in a tube with varying heights?

[manimaran1605]

Homework Statement

Consider a tube of uniform cross section, let one end (a) of the tube is at height h1 and other end (b) is at height h2, where h2>h. Now an incompressible fluid passing through the tube the workdone to pass the liquid at end (a) P1V1 and workdone to pass the liquid at end (b) is -P2V2. So the net workdone is P1V1-P2V2= pressure energy, am I right? The negative sign indicate that at point (b) resists the motion of fluid at (b) How? What is the reason it resists the motion of fluid at (b)?

 

[Jilang]

You might have to consider doing work against gravity.