A9-ft^3 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.

Ahelical coil spring has a mean diameter of 50 mm, a wire diameter of 5.5 mm and is wound with a pitch of 10 mm. the spring steel has an ultimate strength of 1250 mpa. find the force needed to compress the spring solid and the wire stress in this condition. state whether the spring will return to its initial length.