Math Problem Statement

let k=0.15 and use initial conditions of h(0)=0 to solve integral

Solution

Given k=0.15m/mink = 0.15 \, \text{m/min} and the initial condition h(0)=0h(0) = 0, we can solve the integral to find the function h(t)h(t).

Restating the Differential Equation:

From the previous part, we have:

dhdt=16πh2(30.15h3)\frac{dh}{dt} = \frac{16}{\pi h^2} \left(3 - 0.15 h^3\right)

Separating the variables:

h2dh30.15h3=16πdth^2 \, \frac{dh}{3 - 0.15 h^3} = \frac{16}{\pi} \, dt

Solve the Integral:

To solve this, we integrate both sides. Let's start with the left side:

h230.15h3dh=16πdt\int \frac{h^2}{3 - 0.15 h^3} \, dh = \frac{16}{\pi} \int dt

For simplicity, substitute u=30.15h3u = 3 - 0.15 h^3. Then:

du=0.45h2dhdu = -0.45 h^2 \, dh

So, the integral becomes:

10.451udu=16πt+C-\frac{1}{0.45} \int \frac{1}{u} \, du = \frac{16}{\pi} t + C

Integrating:

10.45lnu=16πt+C-\frac{1}{0.45} \ln |u| = \frac{16}{\pi} t + C

Substituting back u=30.15h3u = 3 - 0.15 h^3:

10.45ln30.15h3=16πt+C-\frac{1}{0.45} \ln |3 - 0.15 h^3| = \frac{16}{\pi} t + C

Simplify this equation:

ln30.15h3=0.4516πt0.45C\ln |3 - 0.15 h^3| = -0.45 \cdot \frac{16}{\pi} t - 0.45C

ln30.15h3=7.2πt+C1\ln |3 - 0.15 h^3| = -\frac{7.2}{\pi} t + C_1

where C1C_1 is a constant.

Exponentiating Both Sides:

Exponentiate both sides to solve for h3h^3:

30.15h3=eC1e7.2πt|3 - 0.15 h^3| = e^{C_1} e^{-\frac{7.2}{\pi} t}

Let eC1=Ae^{C_1} = A (a new constant):

30.15h3=Ae7.2πt3 - 0.15 h^3 = A e^{-\frac{7.2}{\pi} t}

Solve for h3h^3:

h3=3Ae7.2πt0.15h^3 = \frac{3 - A e^{-\frac{7.2}{\pi} t}}{0.15}

h3=203A0.15e7.2πth^3 = \frac{20}{3} - \frac{A}{0.15} e^{-\frac{7.2}{\pi} t}

Taking the cube root:

h(t)=(203A0.15e7.2πt)1/3h(t) = \left(\frac{20}{3} - \frac{A}{0.15} e^{-\frac{7.2}{\pi} t}\right)^{1/3}

Determine AA Using Initial Conditions:

Given h(0)=0h(0) = 0:

0=(203A0.15)1/30 = \left(\frac{20}{3} - \frac{A}{0.15}\right)^{1/3}

Thus,

203=A0.15\frac{20}{3} = \frac{A}{0.15}

A=0.15×203=1A = 0.15 \times \frac{20}{3} = 1

Finally, the function h(t)h(t) becomes:

h(t)=(20310.15e7.2πt)1/3h(t) = \left(\frac{20}{3} - \frac{1}{0.15} e^{-\frac{7.2}{\pi} t}\right)^{1/3}

or simplified:

h(t)=(203203e7.2πt)1/3h(t) = \left(\frac{20}{3} - \frac{20}{3} e^{-\frac{7.2}{\pi} t}\right)^{1/3}

This is the height of water in the tank at any time tt.

Would you like more details or have any questions?

Further questions:

  1. What would happen if the proportionality constant kk were larger or smaller?
  2. How does this function behave as tt becomes very large?
  3. Could we find an approximate time at which the tank is nearly full?
  4. How would this function change if the rate of water input varied over time?
  5. What are the limitations of this model in real-world applications?

Tip: When working with differential equations, always check your solution by plugging it back into the original equation to ensure it satisfies all conditions.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Integration
Exponential Functions

Formulas

Separation of variables
Exponential functions
Cube root

Theorems

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Suitable Grade Level

Advanced Undergraduate