You are asked to help design a streamlined dirigible with a length of 600 m and a diameter of 100 m to cruise at 15 m/sec for excursions for retired professors. Your task is to estimate the power required for each of four engines assuming 100% efficient propellers. You are allowed to make the crude assumption for calculating the drag that the surface can be represented as one side of a flat plate formed by unwrapping a hollow cylinder with the same length a diameter. You estimate is about: a. 20 horsepower
b. 200 horsepower
c. 2000 horsepower
d. 2 horsepower

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.