In the context of mechanical systems, what does the term efficiency mean? O A. the factor by which a machine multiplies a force OB the ratio of a machine's power to the force of its input Ос. the rate at which a machine performis work OD the rate at which a machine consumes energy OE. the ratio of the work output of a machine to the work input

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.