A shock wave from an explosion travels at Mach 3 towards a building. The shock reflects from the building wall and travels back in the direction it came from. There is a pile of firewood outside the building that experiences both the incident and reflected shocks. You can treat both as normal shocks. Given the wood has an auto-ignition temperature of 800K (i. e., the temperature at which it will spontaneously ignite), does the wood ignite? When does it ignite (i. e., after the passage of the first shock or the second shock or never?) Before the explosion happened the conditions near the building are 300K and 1 atm pressure.

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?