You are out of gas in the desert and you accidently dropped your phone battery down an Abandoned oil well. You have a charged car battery (12 volts) and a bunch of resistors and wire. You want to power your cell phone with this battery but the cell phone only operates if it has 3.6 Volts across its power terminals. (3.7 Volts will destroy the phone and 3.5 will fail to operate the phone.) If the cell phone uses 0.15 Amperes in all modes, design a circuit that will operate your cell phone from this car battery and let you call for help.

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.