Acompany specification calls for a steel component to have a minimum tensile strength of 1240 mpa. tension tests are conducted on selected samples, but all components are also subjected to vickers hardness testing. (a) what hv (in kgf/mm2) is the minimum acceptable value? (b) if hardness is measured using rockwell c hardness test, what is the minimum hrc value that is acceptable?

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 the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct.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