Small, slowly moving spherical particles experience a drag force given by Stokes' law: where r is the radius of the particle, is its speed, and η is the coefficient of viscosity of the fluid medium. (a) Estimate the terminal speed of a spherical pollution particle of radius 1.00 x 10-5 m and density of 2000 kg/m3. (b) Assuming that the air is still and that η is 1.80 x 0-5 N · s/m2, estimate the time it takes for such a particle to fall from a height of 100 m.