On the first floor of the school building, the barometer shows a pressure of 755 mm Hg

On the first floor of the school building, the barometer shows a pressure of 755 mm Hg, and on the roof 753 mm Hg. Determine the height of the building?

Given:

P1 = 755 mm Hg column – air pressure on the first floor of the building;

P2 = 753 mm Hg column – air pressure on the roof of the building;

ro = 1.3 kg / m3 (kilogram per cubic meter) – air density;

ro1 = 13500 kg / m3 is the density of mercury.

It is required to determine h (meter) – the height of the building.

Let’s find the pressure difference between the roof and the first floor:

dP = P1 – P2 = 755 – 753 = 2 mm Hg = 0.002 meters Hg.

Then:

ro1 * dP * g = ro * g * h;

ro1 * dP = ro * h;

h = ro1 * dP / ro = 13500 * 0.002 / 1.3 = 27 / 1.3 = 21 meters (the result has been rounded to the nearest whole).

Answer: the height of the building is 21 meters.