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

Atmospheric pressure = 76 cm of Hg

Change in pressure = 76 cm of Hg – 70 cm of Hg

= 6 cm of Hg

Pressure falls by 10 mm (= 1 cm) of Hg for every 120 m of ascent,

Therefore, for 6 cm of Hg we get,

120 × 6 = 720

Hence, the height of the hill = 720 m

The assumption made is that the atmospheric pressure falls linearly with ascent.