a ball of mass o.1kg, travelling at 4m/s, hits a smooth billiard cushion normally and rebounds at 4m/s. calculate the force on impact if the time of impact is 0.1s

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?