A14-ft3 tank contains oxygen initially at 14.7 psia and 80°f. a paddle wheel within the tank is rotated until the pressure inside rises to 20 psia. during the process 20 btu of heat is lost to the surroundings. determine the paddle-wheel work done. neglect the energy stored in the paddle wheel. the gas constant and molar mass of oxygen are r = 0.3353 psia·ft3/lbm·r and m = 32 lbm/lbmol. the specific heat of oxygen at the average temperature of tavg = (735 + 540)/2 = 638 r is cv ,avg= 0.160 btu/lbm·r.