A long plank XY lies on the ground. A load of 120 N is placed on it. at a distance of 0.50 m from the end as shown. End Y is lifted off the ground. The upward force needed to do this is 65 . In the diagram, W is the weight of the plank, acting as its mid-point. What is the value of W.

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?