Ahelical compression spring is to be made of oil-tempered wire of 4-mm diameter with a spring index of c = 10. the spring is to operate inside a hole, so buckling is not a problem and the ends can be left plain. the free length of the spring should be 80 mm. a force of 50 n should deflect the spring 15 mm. (a) determine the spring rate. (b) determine the minimum hole diameter for the spring to operate in. (c) determine the total number of coils needed. (d) determine the solid length. (e) determine a static factor of safety based on the yielding of the spring if it is compressed to its solid length.

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?