An alloy is evaluated for potential creep deformation in a short-term laboratory experiment. the creep rate is found to be 1% per hour at 800°c and 0.055% per hour at 700°c.
(a) calculate the activation energy for creep in this temperature range.
(b) estimate the creep rate to be expected at the service temperature of 500°c.

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 the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct.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