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?

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

Correct Answer:

Option B – 570mmHg

Explanation

(p – 760)/(0 – 760) = (h – 0)/(80 – 0)
∴ (p – 760)/-760 = (20 – 0)/80
80(p-760) = -760(20-0)
∴80p – 60800 = -15200
80p = 60800 – 15200
80p = 45600
∴ p = 45600/80
p = 570mmHg