Compare the settling time of the following particles in a quiescent mine atmosphere. Assume that the particles are released at a height of 2 m. a) A rock particle with a diameter of 3 um and a specific gravity of 2.40 g/cm3. b) A coal particle with a diameter of 3 um and a specific gravity of 1.40 g/cm. c). A diesel particle 0.3 m in diameter with a specific gravity of 0.50 g/cm. Assume that the mean free path for air is 0.066 m.