Avolcanic plume puts ash into the atmosphere to altitude of 1m. the characteristic ash particle is a sphere with a diameter of 40 um and has a density of 1000 kg/m^3. consider a single ash particle in isolation that is travelling vertically at its terminal velocity (i. e. no acceleration). assume the density and kinematic viscosity of the air are independent of altitude and is given ,ρ=07kg/m3 and v= 1.5 x 10° m2/s. the drag coefficient is given by stokes' relation: cd =24/re. which of the following answers is closest to the length of time it takes for the particle to settle to the ground? a) 2 hours b) 53 hours c) 33 hours d) 21 hours

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?