A sweet is modelled as a sphere of radius 10mm and is sucked. After five minutes, the radius has decreased to 7mm. The rate of decrease of the radius is inversely proportional to the square of the radius. How long does it take for the sweet to dissolve?
dr/dt propto -1/r^2 and integrate to find equation linking radius and time with boundary conditions. Set r = 0, answer is 7mins 37 seconds.
