Ok so I've been given this problem for one of my classes (see attatchment) : I haven't done much with differential equations before and I'm a bit stuck. What has been putting me off is the fact that it says the vessel has a constant cross sectional area A. which I am guessing is the grey shaded area. I don't understand how whether the differential equation is meant to include this A term. Surely it can't be constant if the height of the water varies? Any help would be greatly appreaciated.