Chapter 9: Problem 25
Find the solution \(y(t)\) by recognizing each differential equation as determining unlimited, limited, or logistic growth, and then finding the constants. $$ \begin{array}{l} y^{\prime}=2-0.01 y \\ y(0)=0 \end{array} $$
Short Answer
Expert verified
The solution is \( y(t) = \frac{200}{1 + e^{-0.01t}} \).
Step by step solution
01
Identify the Type of Growth
Examine the given differential equation \( y' = 2 - 0.01y \). This equation resembles the standard form for a logistic differential equation, which is \( y' = r(K-y) \) or \( y' = ay - by^2 \). However, in this case, it fits the equation for limited growth \( y' = rK - ry \), indicating limited growth due to the presence of a negative term \(-0.01y\).
02
Recognize the Solution Form
Limited growth problems have solutions in the form \( y(t) = \frac{K}{1 + Ce^{-rt}} \). Here, \( K \) is the carrying capacity (the maximum value for \( y \)), and \( C \) is the integration constant determined by initial conditions.
03
Determine the Constants
First, identify the constants in the differential equation. Comparing \( y' = 2 - 0.01y \) with the standard form \( y' = rK - ry \), we can set \( rK = 2 \) and \( r = 0.01 \). Thus, \( K = \frac{2}{0.01} = 200 \).
04
Apply Initial Condition
Use the initial condition \( y(0) = 0 \) to determine the constant \( C \) in \( y(t) = \frac{200}{1 + Ce^{-0.01t}} \). Substitute \( t = 0 \) and \( y = 0 \): \( 0 = \frac{200}{1 + C} \). This gives \( C = 1 \).
05
Write the General Solution
Substituting the constants back into the solution form gives \( y(t) = \frac{200}{1 + e^{-0.01t}} \). This is the expression for \( y(t) \) satisfying the initial condition and the differential equation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Limited Growth Model
In differential equations, the concept of a limited growth model plays a crucial role in understanding situations where growth is not unlimited. The given differential equation, \( y' = 2 - 0.01y \), falls under this category. A limited growth model suggests that there is a maximum or carrying capacity \( K \) that a system approaches over time. In this model, growth slows down as the system approaches \( K \), leading to a more realistic description of scenarios like population growth, where resources impose limits.In our example, the term \(-0.01y\) represents this limitation. It reduces the rate of increase as \( y \) becomes larger, which helps prevent \( y \) from growing without bound. The presence of this term confirms it is a limited growth model, often leading to a stable equilibrium.The standard solution for the limited growth model is \( y(t) = \frac{K}{1 + Ce^{-rt}} \), where \( K \) is the carrying capacity and \( C \) is the integration constant determined by initial conditions. This solution formula helps predict how the system behaves over time, staying bounded while getting closer to \( K \).
Initial Conditions
Initial conditions are vital in solving differential equations, as they determine the specific solution that fits a particular scenario. In our exercise, the initial condition given is \( y(0) = 0 \). This condition signifies the starting point of the system; in practical terms, it could represent the initial population size or concentration level.By applying this initial condition to the solution form \( y(t) = \frac{200}{1 + Ce^{-0.01t}} \), we can determine the value for \( C \), the integration constant. Substituting \( t = 0 \) and \( y = 0 \) into the equation gives:
- \( 0 = \frac{200}{1 + C} \)
- This equation implies \( C = 1 \)
Logistic Differential Equation
Although the differential equation \( y' = 2 - 0.01y \) is primarily described as a limited growth model in this exercise, it still bears similarities with a logistic differential equation. Logistic differential equations are characterized by their structure \( y' = ay - by^2 \), where they typically model population growth with initial rapid growth followed by a level-off as resources become scarce.While our equation does not have the \( by^2 \) term, it can be mistaken for a logistic model due to its limiting behavior and its potential to be adapted if conditions involve quadratic decay factors. Moreover, both models accommodate the idea of a carrying capacity \( K \). In this case, \( K = 200 \), derived from setting \( rK = 2 \) and \( r = 0.01 \).Creating the logistic-like solution from our limited growth form highlights their shared attribute of stabilizing growth patterns as they approach a maximum value. This concept not only aids in mathematical modeling but also gives practical insights into real-world systems that exhibit such growth behavior due to environmental constraints or other factors.