Two piers, a and b, are located on a river. b is 1500 m downstream from a. two friends must make round trips from pier a to pier b and return. one rows a boat at a constant speed of 4.50 km/h relative to the water. the other walks on the shore at a constant speed of 4.50 km/h. the velocity of the river is 2.60 km/h in the direction from a to b. how much time does it take each person to make the round trip?

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?