Hints：

S=1/2 at^2

I excused myself for interrupting him and asked him to go on. In the next minute, he dashed off his answer, which read: "Take the barometer to the top of the building and lean over the edge of the roof. Drop the barometer and time its fall with a stop watch. Then, using the formula S=1/2 at^2 calculate the height of the building." At this point, I asked my colleague if he would give up. He nodded yes, and I gave the student almost full credit. When I left my colleague's office, I recalled that the student had said that he had other answers to the problem. I was curious, so I asked him what they were. "Oh, yes," said the student. "There are many ways of getting the height of a tall building with the aid of a barometer. For example, you could take the barometer out in a sunny day and measure the height of the barometer, the length of its shadow, and the length of the shadow of the building, and by the use of a simple proportion, determine the height of the building. The beauty of this method is that you don't have to drop the barometer and break it." "Fine," I said. "Any more?"