A water tank is obtained by revolving the curve y = kx4, k > 0, about the

Question:

A water tank is obtained by revolving the curve y = kx4, k > 0, about the y-axis.
(a) Find V (y), the volume of water in the tank as a function of its depth y.
(b) Water drains through a small hole according to Torricelli's Law (dV/dt = -m√y). Show that the water level falls at a constant rate.