What two words are missing? An underground pipe is suspected to contain a blockage. A radioactive tracer is put into the pipe to assess the situation. The diagram shows the readings on a radioactivity detector different points above the ground. The readings never reach zero because is being detected.

On a mild saturday morning while people are working inside, the furnace keeps the temperature inside the building at 23degreesc. at noon the furnace is turned off, and the people go home. the temperature outside is a constant 16degreesc for the rest of the afternoon. if the time constant for the building is 3 hr, when will the temperature inside the building reach 18degreesc? if some windows are left open and the time constant drops to 2 hr, when will the temperature inside reach 18degreesc?