Consider a cylindrical water tank of constant cross section \(A .\) Water is
pumped into the tank at a constant rate \(k\) and leaks out through a small hole
of area \(a\) in the bottom of the tank. From Torricelli's theorem in
hydrodynamics it follows that the rate at which water flows through the hole
is \(\alpha a \sqrt{2 g h},\) where \(h\) is the current depth of water in the
tank, \(g\) is the acceleration due to gravity, and \(\alpha\) is a contraction
coefficient that satisfies \(0.5 \leq \alpha \leq 1.0 .\)
(a) Show that the depth of water in the tank at any time satisfies the
equation \(-\)
$$
d h / d t=(k-\alpha a \sqrt{2 g h}) / A .
$$
(b) Determine the equilibrium depth \(h_{e}\) of water and show that it it is
asymptotically stable. Observe that \(h_{e}\) does not depend on \(A .\)