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The rate at which barometric pressure decreases with altitude is proportional to the barometric pressure at that altitude. If the barometric pressure is measured in inches of mercury, and the altitude in feet, then the constant of proportionality is \(3.7 \cdot 10^{-5} .\) The barometric pressure at sea level is 29.92 inches of mercury. (a) Calculate the barometric pressure at the top of Mount Whitney, 14,500 feet (the highest mountain in the US outside Alaska), and at the top of Mount Everest, 29,000 feet (the highest mountain in the world). (b) People cannot easily survive at a pressure below 15 inches of mercury. What is the highest altitude to which people can safely go?

Short Answer

Expert verified
(a) 16.57 inches at Mount Whitney, 10.12 inches at Mount Everest. (b) Maximum safe altitude: 19,135 feet.

Step by step solution

01

Understanding the Differential Equation

The rate at which barometric pressure decreases with altitude is proportional to the pressure itself. This situation can be modeled by a differential equation: \( \frac{dP}{dh} = -kP \), where \( P \) is the barometric pressure and \( h \) is the altitude. Given that the constant of proportionality \( k \) is \( 3.7 \times 10^{-5} \). The negative sign indicates that the pressure decreases as altitude increases.
02

Solving the Differential Equation

To solve \( \frac{dP}{dh} = -3.7 \times 10^{-5} P \), we separate variables and integrate: \[ \int \frac{1}{P} \, dP = -3.7 \times 10^{-5} \int \, dh \] Integrating both sides gives: \[ \ln |P| = -3.7 \times 10^{-5} h + C \] Exponentiating both sides results in: \[ P = Ce^{-3.7 \times 10^{-5}h} \] Where \( C \) is the integration constant.
03

Determining the Constant with Initial Condition

At sea level (\( h = 0 \)), the barometric pressure is 29.92 inches of mercury. We use this to find \( C \): \[ 29.92 = Ce^{-3.7 \times 10^{-5} \times 0} \Rightarrow C = 29.92 \]Thus, the pressure as a function of altitude is: \[ P(h) = 29.92 e^{-3.7 \times 10^{-5}h} \]
04

Calculating Pressure on Mount Whitney

For Mount Whitney at 14,500 feet, substitute \( h = 14500 \) into the pressure function: \[ P(14500) = 29.92 e^{-3.7 \times 10^{-5} \times 14500} \] \[ P(14500) \approx 16.57 \] inches of mercury.
05

Calculating Pressure on Mount Everest

For Mount Everest at 29,000 feet, substitute \( h = 29000 \) into the pressure function: \[ P(29000) = 29.92 e^{-3.7 \times 10^{-5} \times 29000} \] \[ P(29000) \approx 10.12 \] inches of mercury.
06

Finding Safe Altitude for Human Survival

People cannot easily survive at a pressure below 15 inches of mercury. Set the function equal to 15 and solve for \( h \): \[ 15 = 29.92 e^{-3.7 \times 10^{-5} h} \] Divide both sides by 29.92: \[ e^{-3.7 \times 10^{-5} h} = \frac{15}{29.92} \] Taking natural log of both sides gives: \[ -3.7 \times 10^{-5} h = \ln(\frac{15}{29.92}) \] Solve for \( h \): \[ h \approx \frac{\ln(\frac{15}{29.92})}{-3.7 \times 10^{-5}} \approx 19135 \] feet.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Barometric Pressure
Barometric pressure refers to the force exerted by the atmosphere on a given surface. It is measured in units such as inches of mercury (inHg) or millibars. This pressure is an essential concept in meteorology as it affects weather patterns and altitude conditions.

Typically, the standard barometric pressure at sea level is about 29.92 inches of mercury. As one moves higher in altitude, the barometric pressure decreases. This is because there is less air above a certain level to push downwards.

Changes in barometric pressure can also predict weather changes. For instance, a sudden drop might indicate that a storm is approaching. Understanding how barometric pressure behaves is fundamental for forecasting weather and assessing environmental conditions.
Altitude
Altitude refers to the height of an object or point in relation to sea level or ground level. In the context of this exercise, we're exploring how altitude correlates with barometric pressure as we climb higher above sea level.

As altitude increases, the atmospheric pressure decreases because there is less air above and consequently less weight pushing down. This natural reduction is a key reason why high-altitude areas experience lower air pressure than areas at or near sea level.

It is important to consider altitude when predicting weather conditions, calculating the boiling point of water, or determining the performance of aircraft and other technologies.
Exponential Decay
Exponential decay is a process where a quantity decreases at a rate proportional to its current value. In mathematical terms, this is often represented using equations like the differential equation from our exercise.

In this context, the decrease in barometric pressure with altitude can be described by exponential decay. The pressure decreases rapidly at first and then more slowly as altitude increases. This concept is crucial for predicting how pressure changes under different environmental conditions.

Exponential decay is seen in various fields, from the natural sciences in processes like radioactive decay to economics where it might describe depreciation of assets over time.
Integration
Integration is a fundamental concept in calculus, representing the process of finding the accumulated sum or area under a curve. In our exercise, we use integration to solve a differential equation modeling the rate of pressure change with altitude.

The integration process allows us to determine a function that describes how barometric pressure varies with altitude. By integrating the differential equation, we find that the pressure function is an exponential one, showing how integration transforms a rate of change into an overall equation.

Understanding integration is pivotal in solving real-world problems involving areas, volumes, and other situations where cumulative values need to be calculated.
Constant of Proportionality
The constant of proportionality is a constant factor that describes the relationship between two variables that are directly proportional to each other. In the exercise, it is denoted by the symbol \( k \) in the differential equation.

The constant \( k = 3.7 \times 10^{-5} \) quantifies how fast the barometric pressure decreases with an increase in altitude. A larger value would imply a faster rate of decrease and vice versa.

This constant provides a quantitative measure that helps in predicting and calculating the pressure at various altitudes, making it a crucial element in formulating the solution to the problem. Calculating this constant is often the first step in analyzing the relationship between changing quantities.

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