Question

At sea level, the atmospheric pressure is 76 cm of Hg. If air pressure falls by 10 mm of Hg per 120m of ascent, what is the height of a hill where the barometer reads 70 cm Hg. State the assumption made by you.

Answer 1

Atmospheric pressure , P = 76 cm Hg

Rate at which pressure falls = 10 mm of Hg per 120 m of ascent = 1 cm of Hg per 120 m of ascent

Let h be the height of the hill.

Pressure at hill , P' = 70 cm Hg

Total fall in pressure = P - P' = (76 - 70) cm Hg = 6 cm Hg

Now , fall in pressure is 1 cm Hg for every 120 m increase in height

Thus , if the fall in pressure is 6 cm Hg , increase in height shall be (6 × 120)m = 720 m

∴ Height of the hill = 720 m