MECHANICAL PROPERTIES OF FLUIDS

In Millikan’s oil drop experiment, what is the terminal speed of an uncharged drop of radius 2.0 × 10–⁵ m and density 1.2 × 10³kg m–³. Take the viscosity of air at the temperature of the experiment to be 1.8 × 10–5 Pa s. How much is the viscous force on the drop at that speed ? Neglect buoyancy of the drop due to air.