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The air in a room \(50 \mathrm{ft}\) by \(20 \mathrm{ft}\) by \(8 \mathrm{ft}\) tests \(0.2 \%\) carbon dioxide. Starting at \(t=0\). outside air testing \(0.05 \%\) carbon dioxide is admitted to the room. How many cubic feet of this outside air must be admitted per minute in order that the air in the room test \(0.1 \%\) at the end of \(30 \mathrm{~min}\) ?

Short Answer

Expert verified
To find the required volume of outside air per minute (\(V_\text{outside}\)) to change the CO2 percentage in the room from 0.2% to 0.1% after 30 minutes, use the following formula: $$ V_\text{outside} = V_\text{room} * \frac{1}{1.5} $$ Substitute the given dimensions of the room (50 ft by 20 ft by 8 ft) and solve: $$ V_\text{outside} = 50 * 20 * 8 * \frac{1}{1.5} $$ After calculating, \(V_\text{outside}\) is approximately 533.33 cubic feet of outside air per minute.

Step by step solution

01

Find the volume of the room

First, let's find the volume of the room. To do this, you can multiply the dimensions of the room: Length × Width × Height. $$ V_\text{room} = 50~\text{ft} * 20~\text{ft} * 8~\text{ft} $$
02

Calculate the initial and final amount of CO2

To see how the amount of CO2 will change in the room, let's calculate the number of cubic feet of CO2 initially in the room and the desired number of cubic feet of CO2 at the end of 30 minutes. Initial CO2 amount: $$ V_\text{CO2-initial} = V_\text{room} * 0.002 $$ Final CO2 amount: $$ V_\text{CO2-final} = V_\text{room} * 0.001 $$
03

Set up an equation for change in CO2

We need to find how many cubic feet of outside air (which contains 0.05% carbon dioxide) must be admitted to the room to change the CO2 percentage from the initial to the final amount in 30 minutes. Let \(V_\text{outside}\) be the volume of outside air admitted per minute. We will set an equation for the total amount of CO2 in the room at the end of 30 minutes in terms of \(V_\text{outside}\). At the end of 30 minutes: $$ V_\text{CO2-final} = V_\text{CO2-initial} - 30 * 0.002 * V_\text{outside} + 30 * 0.0005 * V_\text{outside} $$
04

Solve for V_outside

Now, we can solve this equation for the required volume of outside air per minute (\(V_\text{outside}\)). $$ V_\text{CO2-final} - V_\text{CO2-initial} = 30 * 0.0005 * V_\text{outside} - 30 * 0.002 * V_\text{outside} $$ Divide the equation by 30 to simplify: $$ \frac{V_\text{CO2-final} - V_\text{CO2-initial}}{30} = 0.0005 * V_\text{outside} - 0.002 * V_\text{outside} $$ Rearrange the equation to find \(V_\text{outside}\): $$ V_\text{outside} = \frac{V_\text{CO2-final} - V_\text{CO2-initial}}{0.0005 - 0.002} $$
05

Substitute the values and find the answer

Now substitute the values of \(V_\text{CO2-final}\) and \(V_\text{CO2-initial}\), which we got in Step 2, and solve for \(V_\text{outside}\). $$ V_\text{outside} = \frac{V_\text{room} * 0.001 - V_\text{room} * 0.002}{0.0005 - 0.002} $$ Simplify to find the final answer: $$ V_\text{outside} = \frac{-V_\text{room} * 0.001}{-0.0015} $$ $$ V_\text{outside} = V_\text{room} * \frac{1}{1.5} $$ Finally, substitute the room volume back: $$ V_\text{outside} = 50 * 20 * 8 * \frac{1}{1.5} $$ This will give you the required volume of outside air per minute.

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Key Concepts

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

Differential Equations
Differential equations are mathematical tools that describe relationships involving rates of change and their associated functions. These versatile equations come into play especially in modelling the behaviour of physical systems as they change over time. In our carbon dioxide ventilation problem, we can think of the concentration of CO2 as a function that changes over time due to the continuous addition of outside air. When we establish a formula that equates the rate of change of CO2 concentration to the flow rate of the outside air, we are essentially setting up a differential equation. This equation will then allow us to determine the volume of air needed to achieve a particular concentration change, which is exactly what's required to solve this ventilation problem.

Rate of Change
The concept of 'rate of change' is a fundamental piece of understanding differential equations. It refers to how quickly or slowly something changes over time or another variable. In our problem, the rate of change is concerned with how the concentration of carbon dioxide changes within the room as outside air is introduced. Since the outside air has a lower concentration of CO2, it dilutes the room's CO2 concentration. The rate at which this concentration changes is directly proportional to the volume of air introduced per minute. The careful manipulation of this rate of change is key to ensuring that the room meets the desired CO2 concentration after 30 minutes.

Initial Value Problem
An initial value problem is a type of differential equation that not only requires you to find a general solution but also needs one that satisfies specific initial conditions. In the context of our ventilation problem, the initial condition is the initial CO2 concentration in the room (0.2%). The goal is to apply the right volume of outside air to move from this initial state to a final desired concentration (0.1%) after a certain time (30 minutes). By including this initial state in our calculations, we ensure that the solution is tailored exactly to the situation at hand, leading to an accurate and practical answer.

Volume Calculation
Volume calculation is a practical and essential math skill, especially in problems related to physical spaces and substances filling them. In our scenario, calculating the volume of the room is our starting point. Only after knowing this can we begin to understand and manipulate the CO2 concentration within this space. By multiplying the room's length, width, and height (50ft x 20ft x 8ft), we determine the volume of space we are dealing with. This value is then crucial for calculating the initial and final volumes of CO2, and subsequently, the volume of outside air needed to adjust the CO2 concentration to the target percentage over the specified time frame.

Understanding these calculations ensures we approach our problem methodically, resulting in precise and feasible solutions for real-world situations like proper ventilation in enclosed spaces.

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