Problem 4 (6.25 pts): A grain of pollen has a radius of approximately 15 microns (1.5 x 107 m) and a mass of ap- proximately 1.7 x 107! kg. Calculate the terminal speed of a pollen grain falling down to the bottom of a lake. The viscosity of water is 6.5 x 10~* kg/m-s. A) 164 x 1072 m/s B) 0.9 x 107 m/s C) 34 x1072 m/s D) 9.5 x 1071 m/s