7.32 experimentally, it has been observed for single crystals of a number of metals that the critical resolved shear stress τcrss is a function of the dislocation density rhod aswhere τ0 and a are constants. for copper, the critical resolved shear stress is 2.10 mpa (305 psi) at a dislocation density of 105 mm-2. if it is known that the value of a for copper is 6.35  10-3 mpa-mm (0.92 psi-mm), compute the crss at a dislocation density of 107 mm-2.