/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 16 Growing Sand Pile Sand falls fro... [FREE SOLUTION] | 91Ó°ÊÓ

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Growing Sand Pile Sand falls from a conveyor belt at the rate of 10 \(\mathrm{m}^{3} / \mathrm{min}\) onto the top of a conical pile. The height of the pile is always three-eighths of the base diameter. How fast are the (a) height and (b) radius changing when the pile is 4 \(\mathrm{m}\) high? Give your answer in \(\mathrm{cm} / \mathrm{min.}\)

Short Answer

Expert verified
The height \(h\) and radius \(r\) of the pile are changing at \(dh/dt = -1.67 \mathrm{cm} / \mathrm{min}\) and \(dr/dt = 3.33 \mathrm{cm} / \mathrm{min}\) respectively when the pile is 4 m high.

Step by step solution

01

Write the Volume Formula for a Cone

The volume \(V\) of a cone is given by \(V = 1/3 \pi r^{2}h\), where \(r\) is the radius and \(h\) is the height.
02

Writing height in terms of radius

Given that the height \(h\) of the pile is always three-eighths of the base diameter, and knowing that the diameter = 2r, we could express h in the terms of r as \(h=\frac{3}{4}r\). Substitute this value of h in the volume formula of the cone. This leads to \(V = 1/3 \pi r^{2} (\frac{3}{4}r) = \frac{1}{4}\pi r^{3}\), a relation between the volume and radius of the cone.
03

Differentiate Both Sides with Respect to Time

Differentiating the equation from step 2 with respect to \(t\) will help us find the rates of change. This results in \(dV/dt = \frac{3}{4}\pi r^{2} dr/dt\), where \(dV/dt\) is the rate of change of volume (10 \(\mathrm{m}^{3} / \mathrm{min}\) or 1000000 \(\mathrm{cm}^{3} / \mathrm{min}\)) and \(dr/dt\) is the rate of change of the radius that we're trying to find. We can rewrite the equation to isolate \(dr/dt\), resulting in \(dr/dt = \frac{4 dV/dt}{3 \pi r^{2}}\).
04

Solve for \(dr/dt\)

Substitute the given values of \(dV/dt = 1000000 \mathrm{cm}^{3} / \mathrm{min}\) and \(r = 400cm\), we find \(dr/dt = \frac{4 * 1000000}{3 \pi 400^{2}} = 3.33 \mathrm{cm} / \mathrm{min}.\)
05

Solve for \(dh/dt\)

Using the relationship \(dh/dt = -1/2dr/dt\) obtained from the initial formula \(dh/dt = -3/8dD/dt\), we substitute \(dr/dt = 3.33 \mathrm{cm} / \mathrm{min}\) to calculate \(dh/dt = -1/2 * 3.33 = -1.67 \mathrm{cm} / \mathrm{min}.\)

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Key Concepts

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

Volume of a Cone
Understanding the volume of a cone is essential in solving many calculus problems, especially when dealing with three-dimensional objects. A cone is a solid with a circular base and a single vertex that is not in the plane of the base. The volume formula for a cone is given by \(V = \frac{1}{3}\pi r^{2}h\), where \(r\) is the radius of the base and \(h\) is the height from the base to the vertex. It's crucial to comprehend this relationship because it sets the foundation for finding out how the volume changes with time when the dimensions of the cone change, as in the case with our growing sand pile problem.

When solving related rates problems that involve cones, students should remember to express all the related variables in terms of a single variable whenever possible. For example, in the exercise, the height \(h\) is correlated to the radius \(r\) through a given ratio. Such relationships are key to simplifying the problem and setting up our differentiation equation correctly.
Differentiation with Respect to Time
In calculus, the concept of differentiation with respect to time, often represented by \(\frac{d}{dt}\), is used to find the rate at which certain quantities change over time. This process is fundamental to solving related rates problems. Differentiation allows us to calculate the instantaneous rate of change, which is the basis for understanding how the characteristics of objects, like the volume of our conical sand pile, evolve as time progresses.

To differentiate an equation with respect to time that contains more than one variable, we apply the chain rule. This rule acknowledges that the variables themselves are functions of time, even if we don't have explicit formulas for those functions. When we differentiate, we generate derivatives of these variables with respect to time, which in the case of radius and height changes is represented as \(\frac{dr}{dt}\) and \(\frac{dh}{dt}\), respectively.
Cones and Cylinders
Cones and cylinders are similar in that they both have circular bases, but a cone tapers to a point while a cylinder does not. They are important shapes in geometry and thus in calculus exercises due to their real-world applications, like tanks, containers, and piles. When we deal with rates of change involving cylinders, it's typically the volume or the height that is changing. However, with cones, the situation can be more complex because a change in height usually involves a simultaneous change in the radius.

This interconnectedness of radius and height in cones is precisely what makes related rates problems involving cones more challenging and interesting. Recognizing the shape we're dealing with and the relationship between its dimensions will guide our application of formulas and differentiation.
Rate of Change
The rate of change is a measure of how a quantity changes with respect to another variable, such as time. In physics and engineering, rates of change are omnipresent, reflecting how physical quantities evolve. In calculus, we often focus on the rate of change with respect to time, indicated by \(\frac{d}{dt}\), as it displays dynamism in otherwise static formulas.

In our exercise, we calculate the rates at which the height and radius of a sand pile change. It's important to remember that rates can be positive or negative, indicating increase or decrease, which is crucial when interpreting the problem correctly. For instance, a negative rate of change for the height might indicate that the height is decreasing as the pile spreads out, even if the total volume is increasing. Grasping this concept ensures that we can solve for, and understand, the implications of \(\frac{dh}{dt}\) and \(\frac{dr}{dt}\) in real-world scenarios.

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Most popular questions from this chapter

Stiffness of a Beam The stiffness S of a rectangular beam is proportional to its width times the cube of its depth. (a) Find the dimensions of the stiffest beam that can be cut from a 12-in. diameter cylindrical log. (b) Writing to Learn Graph \(S\) as a function of the beam's width \(w,\) assuming the proportionality constant to be \(k=1 .\) Reconcile what you see with your answer in part (a). (c) Writing to Learn On the same screen, graph \(S\) as a function of the beam's depth \(d,\) again taking \(k=1 .\) Compare the graphs with one another and with your answer in part (a). What would be the effect of changing to some other value of \(k ?\) Try it.

Finding Parameter Values Show that \(f(x)=x^{2}+(a / x)\) cannot have a local maximum for any value of \(a .\)

You may use a graphing calculator to solve the following problems. True or False If the radius of a circle is expanding at a constant rate, then its circumference is increasing at a constant rate. Justify your answer.

Estimating Volume You can estimate the volume of a sphere by measuring its circumference with a tape measure, dividing by 2\(\pi\) to get the radius, then using the radius in the volume formula. Find how sensitive your volume estimate is to a 1\(/ 8\) in. error in the circumference measurement by filling in the table below for spheres of the given sizes. Use differentials when filling in the last column. $$\begin{array}{|c|c|c|}\hline \text { Sphere Type } & {\text { True Radius }} & {\text { Tape Error Radius Error Volume Error }} \\ \hline \text { Orange } & {2 \text { in. }} & {1 / 8 \text { in. }} \\ \hline \text { Melon } & {4 \text { in. }} & {1 / 8 \text { in. }} \\ \hline \text { Beach Ball } & {7 \text { in. }} & {1 / 8 \text { in. }}\end{array}$$

The Linearization is the Best Linear Approximation Suppose that \(y=f(x)\) is differentiable at \(x=a\) and that \(g(x)=m(x-a)+c(m\) and \(c\) constants). If the error \(E(x)=f(x)-g(x)\) were small enough near \(x=a,\) we might think of using \(g\) as a linear approximation of \(f\) instead of the linearization \(L(x)=f(a)+f^{\prime}(a)(x-a) .\) Show that if we impose on \(g\) the conditions i. \(E(a)=0\) ii. \(\lim _{x \rightarrow a} \frac{E(x)}{x-a}=0\) then \(g(x)=f(a)+f^{\prime}(a)(x-a) .\) Thus, the linearization gives the only linear approximation whose error is both zero at \(x=a\) and negligible in comparison with \((x-a)\) .

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