(b) Use the given formulas for the volume and area (displayed above the diagram) to rewrite the equation in (a) as an equation for h dh (We will call this a related rate equation.) dt and

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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First image is the word problem. Please answer PART B. Please show all steps and explain with clear handwriting. No cursive if possible. 

### Guided Instruction

**(a) Express the assumption that "the rate of change of the volume of water, \( V \), is proportional to the surface area \( A \)."**

Use a proportionality constant \( k \) (which may be named as "porosity"). Is it a positive or a negative constant? Since this is a crucial step, I will just write the answer for you.

\[
\frac{dV}{dt} = kA
\]

**(b) Use the given formulas for volume and area (displayed above the diagram) to rewrite the equation in (a) as an equation for \( h \) and \( \frac{dh}{dt} \). (We will call this a related rate equation.)**

**(c) Solve the related rate equation from (b) for \( \frac{dh}{dt} \) and simplify it.** 

Use this equation to explain why the drain rate \( h' \left( t \right) \) cannot be a constant function unless the filter is completely clogged (that is, unless \( k = 0 \)). [Hint: You may use \( h'' \left( t \right) \) to be able to answer this. There are other ways, too.]

1. Suppose the water is completely drained at a time \( t = t_0 \). Talk about the limits \( \lim_{t \to t_0^-} \left[ h(t) \right] \) and about \( \lim_{t \to t_0^-} \left[ h'(t) \right] \).
2. To answer these, make an assumption that \( h \left( t \right) \) is a monotonically decreasing continuous function (i.e., water doesn't climb back up!), and that \( h \left( t_0 \right) = 0 \). Verify your findings analytically by using the related rate equation.

**(d) Study the concavity of the graph of the function \( h \).**

We do this so we know whether the water level goes down faster and faster or slower and slower. Is the graph of \( h \) always concave up or always concave down or does it have an inflection point? Provide a physical explanation to your finding about the concavity.

**(e) Sketch a reasonable graph of \( h(t) \) and of \( h'(t)
Transcribed Image Text:### Guided Instruction **(a) Express the assumption that "the rate of change of the volume of water, \( V \), is proportional to the surface area \( A \)."** Use a proportionality constant \( k \) (which may be named as "porosity"). Is it a positive or a negative constant? Since this is a crucial step, I will just write the answer for you. \[ \frac{dV}{dt} = kA \] **(b) Use the given formulas for volume and area (displayed above the diagram) to rewrite the equation in (a) as an equation for \( h \) and \( \frac{dh}{dt} \). (We will call this a related rate equation.)** **(c) Solve the related rate equation from (b) for \( \frac{dh}{dt} \) and simplify it.** Use this equation to explain why the drain rate \( h' \left( t \right) \) cannot be a constant function unless the filter is completely clogged (that is, unless \( k = 0 \)). [Hint: You may use \( h'' \left( t \right) \) to be able to answer this. There are other ways, too.] 1. Suppose the water is completely drained at a time \( t = t_0 \). Talk about the limits \( \lim_{t \to t_0^-} \left[ h(t) \right] \) and about \( \lim_{t \to t_0^-} \left[ h'(t) \right] \). 2. To answer these, make an assumption that \( h \left( t \right) \) is a monotonically decreasing continuous function (i.e., water doesn't climb back up!), and that \( h \left( t_0 \right) = 0 \). Verify your findings analytically by using the related rate equation. **(d) Study the concavity of the graph of the function \( h \).** We do this so we know whether the water level goes down faster and faster or slower and slower. Is the graph of \( h \) always concave up or always concave down or does it have an inflection point? Provide a physical explanation to your finding about the concavity. **(e) Sketch a reasonable graph of \( h(t) \) and of \( h'(t)
### Problem Choice 2.1

In this problem, we will consider a filter that is shaped as a lower semi-sphere. The picture below shows a spherical filter with water filled to level \( h \). The following formulas are essential for the completion of this work:

- The volume of water filled to level \( h \) in a spherical bowl with radius \( R \) is given by:
  
  \[
  V = \pi h^2 \left( R - \frac{h}{3} \right)
  \]

- Another crucial formula is \( A = 2\pi R h \), for the surface area of the part of the sphere that is in contact with the body of water.

#### Diagram Explanation
The diagram illustrates a semi-spherical bowl with radius \( R \) filled with water to height \( h \). Water is shown dripping from the bottom, indicating the draining process.

We will investigate the relationship between the water level \( h \) and the rate at which this level changes ( \( \frac{dh}{dt} \) ) based on the assumption that the drain rate (the rate at which the volume of the water decreases) is proportional to the surface area of contact. (This is approximately what happens with an actual coffee filter!) Ultimately, we are interested in expressing \( h \) as a function of time \( t \).

Please read on for more detailed instructions below.

### Context

To put your mind in a more concrete context, let's think about a cone-shaped filter. For the filter of any shape, water is drained at a rate that is proportional to the contact area. In the case of a right-angle cone filter, this area is \( \sqrt{2} \pi h^2 \). So,

\[
\frac{dV}{dt} = \sqrt{2} \pi kh^2
\]

for some negative constant \( k \). But, since \( V = \frac{1}{3} \pi h^3 \) (for a right-angle cone), we have

\[
\sqrt{2} \pi kh^2 = \pi h^2 \cdot \frac{dh}{dt} \implies \sqrt{2} k = \frac{dh}{dt}
\]

This tells us that the water level will decrease at a constant rate. In the case of a spherical funnel, will we arrive at a similar conclusion? We
Transcribed Image Text:### Problem Choice 2.1 In this problem, we will consider a filter that is shaped as a lower semi-sphere. The picture below shows a spherical filter with water filled to level \( h \). The following formulas are essential for the completion of this work: - The volume of water filled to level \( h \) in a spherical bowl with radius \( R \) is given by: \[ V = \pi h^2 \left( R - \frac{h}{3} \right) \] - Another crucial formula is \( A = 2\pi R h \), for the surface area of the part of the sphere that is in contact with the body of water. #### Diagram Explanation The diagram illustrates a semi-spherical bowl with radius \( R \) filled with water to height \( h \). Water is shown dripping from the bottom, indicating the draining process. We will investigate the relationship between the water level \( h \) and the rate at which this level changes ( \( \frac{dh}{dt} \) ) based on the assumption that the drain rate (the rate at which the volume of the water decreases) is proportional to the surface area of contact. (This is approximately what happens with an actual coffee filter!) Ultimately, we are interested in expressing \( h \) as a function of time \( t \). Please read on for more detailed instructions below. ### Context To put your mind in a more concrete context, let's think about a cone-shaped filter. For the filter of any shape, water is drained at a rate that is proportional to the contact area. In the case of a right-angle cone filter, this area is \( \sqrt{2} \pi h^2 \). So, \[ \frac{dV}{dt} = \sqrt{2} \pi kh^2 \] for some negative constant \( k \). But, since \( V = \frac{1}{3} \pi h^3 \) (for a right-angle cone), we have \[ \sqrt{2} \pi kh^2 = \pi h^2 \cdot \frac{dh}{dt} \implies \sqrt{2} k = \frac{dh}{dt} \] This tells us that the water level will decrease at a constant rate. In the case of a spherical funnel, will we arrive at a similar conclusion? We
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