Calculate the height of the plane above the ground?

Plane as 63cm of HG while a ground observer records a reading of 75cm of Hg with his barometer. assuming that the density of air is constant, calculate the height of the plane above the ground. (Take the relative densities of air and mercury as 0.00136 and 13.6 respectively

A. 120m
B. 138m
C. 1200m
D. 274m
E. 120,000m

Correct Answer:

Option E – 120,000m

Explanation

Pressure change for air = pressure change for mercury

hpg = Hpg

h x 0.00136 x g = (75 – 63) x 13.6 x g

h= (12×13.6)/0.00136

= 120,000m