Arock sample was placed in a strength-testing machine at a uniform confining force of 10,000 lbf and is compressed axially up to failure point. a force of 12,000 ibf was required for rock failure, and the cross- sectional area and the height of the sample were 2.0 sq in and 1.8 in respectively. the sample failed along a plane that marks a 350 angle with the direction of compressional loading a) construct the mohr's circle using the two principal stresses present b) compute the shear stress present along the plane of failure c) compute the normal stress to the plane of failure. d) compute the angle of internal friction. e) compute the cohesive resistance of the material. f)label the parameters computed in the previous four steps on the mohr's circle construction. using the mohr criterion, compute the compressional force required for rock failure if the sample is placed under a 5,000-psi confining 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?