Chapter U3.9, Problem 7E

Interpretation Introduction

Interpretation: Comprehend the air pressure of 0.5 atm in pounds per square inch at altitude of 18000 ft. Also calculate the weight in pounds on the back of the hand at same altitude.

Concept Introduction:

Conversion factor is ratio that is widely used to describe relation between two different units. In order to convert one unit into another, original unit is multiplied with proper conversion factor to yield new unit.

Answer to Problem 7E

Pressure = $\text{7}{\text{.35 pounds/ in}}^{\text{2}}$

  $\text{Weight =110 lb}$

Explanation of Solution

Given information:

Atmospheric pressure − 0.5 atm

Height = 18000 ft

Atmospheric pressure − 0.5 atm

1 atmosphere = 14.7-pounds/ in²

The average size of a human hand = 15 in²

Convert atm to pounds/ in²:

  $\text{0}\text{.5 atm ×}\frac{\text{14}{\text{.7-pounds/ in}}^{\text{2}}}{\text{1 atm}}\text{ = 7}{\text{.35 pounds/ in}}^{\text{2}}$

Calculate the weight in pounds of the atmosphere pushing down on the back of hand:

  $\begin{array}{l}\text{Weight = Pressure per unit area × Area}\\ \text{Weight = }\frac{\text{7}\text{.35 lb}}{{\text{1 in}}^{\text{2}}}{\text{ × 15 in}}^{\text{2}}\\ \text{Weight =110 lb}\end{array}$

Conclusion

Pressure = $\text{7}{\text{.35 pounds/ in}}^{\text{2}}$

  $\text{Weight =110 lb}$