The height at which the atmosphere ceases to exist is about 80km. If the atmospheric pressure on the ground level is 760mmHg….

The height at which the atmosphere ceases to exist is about 80km. If the atmospheric pressure on the ground level is 760mmHg, the pressure at a height of 20km above the ground level is? (ρm = 13.6g/cm3 ρ = 0.00013g/cm3 )

A. 380mmHg
B. 570mmHg
C. 190mmHg
D. 480mmHg

Correct Answer: Option B

Explanation

ρmhm = ρaha
13.68(760 – p) × 10‾³ = 13 × 10^–5(20 × 10³)

760 – p = (13 × 10−5 × 20 × 10³)/(13.68 × 10‾³) = 19.00 × 10¹

760 – p = 190
p = 760 – 190 = 570mmHg