A speed reducer has 20 deg full depth teeth and consisct of a 20 tooth steel spur pinion driving a 50 tooth cast iron gear. the horse power transmitted is 12 at a pinion speed of 1200 rev/min. for a dimateral pitch of 8 teeth/ in and a face width of 1.5 in find the contact stress. the yuong's modulus of the steel is 30E6 and young's modulus of cast iron is 15E6. use a poisson's ratio of 0.3 for both materials. use equation 14-14 to calc the contact stress in the gear only.

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.