Because a sailboat cannot sail directly into the wind, and traveling straight downwind is usually slow, the shortest sailing
distance is rarely a straight line. thus sailboats tack upwind—the familiar zigzag course—and jibe downwind. a tactician's
decision of when to tack and where to go can determine the outcome of a race. describe the process of tacking a sailboat
as the wind shifts direction. sketch a block diagram depicting tills process.

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.