A small metal sphere of radius 0.5 mm has mass 1.0 × 10^-3 kg is dropped into oil of which the viscosity is 0.36 N s m^-2.  What is the terminal velocity at which it falls?                                                                                                                            

F = mg = 6phrv (P)

F = 1 × 10^-3 kg × 10 m/s = 0.01 N (P)

0.01 = 6 × p × 0.36 × 0.5 × 10^-3 × v (P)

v = 0.01 ÷ 3.39 × 10^-3 = 2.95 m/s (P)