A volcano has erupted, spewing stones, steam, and ash several thousand feet into the atmosphere. After some time, the particles begin to settle to the ground. Consider a nearly spherical ash particle that is 50 microns in diameter, falling in air whose temperature is -50°C and whose pressure is 55 kPa. The density of the particle is 1240 kg/m3. Estimate the terminal velocity of this particle at this altitude.