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.

Refrigerant-134a enters the compressor of a refrigerator as superheated vapor at 0.14 mpa and -10°c at a rate of 0.05 ka/s and leaves at 0.8 mpa and 50°c. the refrigerant is cooied in the condenser to 0.72 mpa and 26'c. it is then throttled to 0.15 mpa. sketch the t-s diagram for the system and evaluate: 6) the rate of heat removai from the refrigerated space (kw), it) the power input to the compressor (kw), ii) the isentropic efficiency of the compressor (%), and iv) the cop of the refrigerator.