How could you use the barometer to determine the height of a building?

Take the barometer to the roof of the building. Drop the barometer from the edge of the roof, and, with your wrist watch or a stop watch, measure the time it takes for the barometer to hit the ground or the street below. Then the height of the roof, in meters, is 4.9 times the square of the time in seconds.

Ireally don’t know

C. it comes from the core of the earth.