A hollow plastic spherical bobber of mass 0.005 kg and volume 50 cm3 floats on the surface of a lake. The bobber supports a submersed fishhook and bait with a combined mass of 0.01 kg and a combined volume of 2 cm3. The density of water is 0.001 kg/cm3. If a fish grabs the bait, find the minimum downward force, Ffish, that it must exert to pull the bobber completely under the surface of the water. You may assume that the apparent weight of the fish is zero.

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?