A common automotive steel has a yield strength of 250 MPa when it is processed to have an average grain diameter of 2.5x10 mm. When the average grain diameter is decreased to 5x10 mm, the yield strength increases to 325 MPa. What is the average grain diameter (mm) when a yield strength of 375 MPa is require

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 the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct.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