A cylinder fitted with aa frictionless piston contains an ideal gas at temperature T and pressire P. The gas exapnds isothermally and reversibly until the pressure is p/3. Ehich statement is true regarding the work done by the gas during expansiona. Equal to the heat absorbed by the gas. b. Equal to the internal energy change of the gas. c Equal to the enthalpy change of the gas. d. Equal to 11 P time the volume change in the gas. e. Greater than the heat absorbed by the gas

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.