Two 0.5 cm-diameter rods of 1020 steel (σts = 395 mpa) are to be joined with a silver braze alloy 0.025 cm thick (σys = 145 mpa) to produce one long rod. the ultimate strength of this brazed structure is found to be approximately 345 mpa. if it is necessary to reduce the diameter of the rods to 0.25 cm with no change to the braze joint itself, will the strength (in mpa units) increase, decrease, or remain the same? if it changes, by how much?

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 the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct.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.