Question

A sphere of diameter D, moving at speed v in air, experiences a quadratic drag force given approximately by FD = (0.25 Ns2/m4) D2 v2, for diameters of few centimetres or more, and speeds of a metre per second or more. Calculate the terminal velocity of a basketball (25 cm diameter, mass 1 kg), and of a grapefruit 10 cm in diameter (assume a density of 1000 kg/m3 for the grapefruit).