Sound waves require a to travel through

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?

The electric field inside a cell membrane is 8.0mn/c. what's the force on a singly charged ion in this field?

The resistance of 100 w bulb is less than resistance of 40 w bulb. explain the reason.