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For the following regions \(R\), determine which is greater- the volume of the solid generated when \(R\) is revolved about the x-axis or about the y-axis. \(R\) is bounded by \(y=1-x^{3}\), the \(x\) -axis, and the \(y\) -axis.

Short Answer

Expert verified
Answer: The volume generated by revolving the region R around the y-axis is greater.

Step by step solution

01

Find the intersections

Region \(R\) is bounded by the curve \(y=1-x^3\), the x-axis (\(y=0\)) and the y-axis (\(x=0\)). To find the points of intersection with the x-axis, set \(y = 0\): \(0 = 1 - x^3\) \(x^3 = 1\) \(x = 1\) The intersection with the x-axis is \((1, 0)\). The intersection with the y-axis is \((0, 1)\). So the region's boundary values are \([0, 1]\) for the x-axis and \([0, 1]\) for the y-axis.
02

Volume by revolving around x-axis

We will use the disk method to find the volume of the solid generated by revolving region \(R\) around the x-axis. The disk method formula for revoling around x-axis is: \(V_x = \pi \int_{a}^{b} y^2 dx \) We have: \(y=1-x^3\), so \(y^2 = (1-x^3)^2\) Now, we integrate from \(x=0\) to \(x=1\): \(V_x = \pi \int_{0}^{1} (1-x^3)^2 dx\)
03

Calculate the integral for revoling around x-axis

Now, we need to calculate the integral: \(V_x = \pi \int_{0}^{1} (1-2x^3+x^6) dx\) \(V_x = \pi [x-\frac{1}{2}x^4+\frac{1}{7}x^7]_0^1\) \(V_x = \pi[1- \frac{1}{2}+\frac{1}{7}]\) \(V_x= \frac{5}{14}\pi\)
04

Volume by revolving around y-axis

We will use the disk method to find the volume of the solid generated by revolving the region \(R\) around the y-axis. We have to rewrite the function in terms of x: \(x = (1-y)^{1/3}\) The disk method formula for revolving around the y-axis is: \(V_y = \pi \int_{c}^{d} x^2 dy \) Now, we integrate from \(y=0\) to \(y=1\): \(V_y = \pi \int_{0}^{1} ((1-y)^{1/3})^2 dy\)
05

Calculate the integral for revolving around y-axis

Now, we need to calculate the integral: \(V_y = \pi \int_{0}^{1} (1-y)^{2/3} dy\) Let's do a substitution: \(u = 1-y\) and \(du=-dy\): \(V_y = -\pi \int_{1}^{0} u^{2/3} du\) This will result in: \(V_y = \pi[\frac{3}{5} u^{5/3} ]_1^0\) \(V_y = \frac{3}{5}\pi\)
06

Compare volumes

Now, we need to compare the volumes of the solids generated by revolving region \(R\) around the x-axis (\(V_x\)) and the y-axis (\(V_y\)): \(V_x = \frac{5}{14}\pi\) \(V_y = \frac{3}{5}\pi\) Since \(\frac{5}{14}\pi < \frac{3}{5}\pi\), the volume of the solid generated by revolving region \(R\) around the y-axis is greater.

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Key Concepts

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

Disk Method
The Disk Method is a technique used in calculus to find the volume of a solid of revolution. This method is particularly useful when a region is revolved around the x-axis or y-axis to form a 3D shape. The core idea is to imagine slicing the solid into a series of thin circular disks. Each disk has a small thickness, and calculating the sum of the volumes of these disks gives the volume of the entire solid.

To apply the disk method, we use the formula:- When revolving around the x-axis: \[ V = \pi \int_{a}^{b} [f(x)]^2 \, dx \] This formula calculates the sum of disks with thickness dx from a to b, where the radius is determined by the function value, \( f(x) \).- When revolving around the y-axis: \[ V = \pi \int_{c}^{d} [g(y)]^2 \, dy \] Here, the disks have thickness dy, with the radius determined by the function \( g(y) \).

The choice between revolving around the x-axis or the y-axis depends on the problem structure, influencing how we express the functions and set integration limits. Understanding the setup is critical for correctly applying the disk method and accurately calculating the volume of the solid.
Integral Calculus
Integral calculus is a branch of calculus focused on accumulation of quantities and the areas under and between curves. Integral calculus is essential in finding areas, volumes, central points, among others. It is especially vital in the context of the disk method, where it helps in calculating volumes of solids of revolution.

To solve such problems, we often convert a geometric area or volume problem into an integration problem, where we sum up infinitesimally small pieces. The definite integral evaluates these sums over a specified interval:
  • The integral \( \int_{a}^{b} f(x) \, dx \) computes the accumulation of the function \( f(x) \) as it spans from \( a \) to \( b \).

  • The process involves finding an antiderivative (inverse of differentiation) that represents the accumulated quantity.

When using integral calculus with the disk method, the task is to determine the antiderivative to evaluate the definite integral, giving us the total volume. Having a solid grasp of integration techniques helps solve complex volume problems efficiently.
Intersection Points
Intersection points are critical in solving problems involving areas and volumes. These are where two or more curves meet, and they define the bounds for integration. In our particular problem, we need to identify where the curve intersects the axes to correctly set up our integral limits.

The given curve in this exercise is \( y = 1 - x^3 \). To locate intersections:
  • For the x-axis intersection, set the function \( y = 0 \) and solve for \( x \): \ \( 0 = 1 - x^3 \Rightarrow x^3 = 1 \Rightarrow x = 1 \)

  • For the y-axis intersection, set \( x = 0 \) and solve for \( y \): \ \( y = 1 - 0^3 = 1 \)

These intersections, \((1,0)\) and \((0,1)\), help define the region and are crucial for deciding the integration limits when applying the disk method. Knowing how to find these points effectively allows for setting up accurate and meaningful integration bounds, leading to the correct calculation of areas or volumes.

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Most popular questions from this chapter

a. Confirm that the linear approximation to \(f(x)=\tanh x\) at \(a=0\) is \(L(x)=x.\) b. Recall that the velocity of a surface wave on the ocean is \(v=\sqrt{\frac{g \lambda}{2 \pi} \tanh \frac{2 \pi d}{\lambda}} .\) In fluid dynamics, shallow water refers to water where the depth-to-wavelength ratio \(d / \lambda<0.05 .\) Use your answer to part (a) to explain why the shallow water velocity equation is \(v=\sqrt{g d}.\) c. Use the shallow-water velocity equation to explain why waves tend to slow down as they approach the shore.

A power line is attached at the same height to two utility poles that are separated by a distance of \(100 \mathrm{ft}\); the power line follows the curve \(f(x)=a \cosh (x / a) .\) Use the following steps to find the value of \(a\) that produces a sag of \(10 \mathrm{ft}\) midway between the poles. Use a coordinate system that places the poles at \(x=\pm 50.\) a. Show that \(a\) satisfies the equation \(\cosh (50 / a)-1=10 / a.\) b. Let \(t=10 / a,\) confirm that the equation in part (a) reduces to \(\cosh 5 t-1=t,\) and solve for \(t\) using a graphing utility. Report your answer accurate to two decimal places. c. Use your answer in part (b) to find \(a\) and then compute the length of the power line.

Find the \(x\) -coordinate of the point(s) of inflection of \(f(x)=\operatorname{sech} x .\) Report exact answers in terms of logarithms (use Theorem 6.10 ).

Find the area of the following regions, expressing your results in terms of the positive integer \(n \geq 2\) Let \(A_{n}\) be the area of the region bounded by \(f(x)=x^{1 / n}\) and \(g(x)=x^{n}\) on the interval \([0,1],\) where \(n\) is a positive integer. Evaluate \(\lim _{n \rightarrow \infty} A_{n}\) and interpret the result.

A quantity grows exponentially according to \(y(t)=y_{0} e^{i t} .\) What is the relationship between \(m, n,\) and \(p\) such that \(y(p)=\sqrt{y(m) y(n)} ?\)

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