/*! 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 44 Evaluate the spherical coordinat... [FREE SOLUTION] | 91Ó°ÊÓ

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Evaluate the spherical coordinate integrals in Exercises \(43-48\) $$ \int_{0}^{2 \pi} \int_{0}^{\pi / 4} \int_{0}^{2}(\rho \cos \phi) \rho^{2} \sin \phi d \rho d \phi d \theta $$

Short Answer

Expert verified
The value of the integral is \(2\pi\).

Step by step solution

01

Identify the Integral Components

The given triple integral is \( \int_{0}^{2 \pi} \int_{0}^{\pi / 4} \int_{0}^{2}(\rho \cos \phi) \rho^{2} \sin \phi \, d \rho \, d \phi \, d \theta \). It needs to be evaluated in spherical coordinates \((\rho, \phi, \theta)\), which refer to the radius, polar angle, and azimuthal angle respectively. Note that the integrand contains \( (\rho \cos \phi) \rho^{2} \sin \phi \).
02

Simplify the Integrand

The integrand is \( (\rho \cos \phi) \rho^{2} \sin \phi \). Simplify it to \( \rho^3 \cos \phi \sin \phi \). The integrand in terms of \( \rho, \phi, \rho \) is organized for integration as \( \rho^3 \cos \phi \sin \phi \).
03

Integrate with Respect to \( \rho \)

First, evaluate the integral with respect to \( \rho \) from 0 to 2:\[\int_{0}^{2} \rho^3 \, d \rho = \left[ \frac{\rho^4}{4} \right]_0^2 = \frac{16}{4} = 4.\]
04

Integrate with Respect to \( \phi \)

With \( \rho \) integrated out, evaluate the integral with respect to \( \phi \) from 0 to \( \pi/4 \):\[\int_{0}^{\pi/4} \cos \phi \sin \phi \, d \phi = \int_{0}^{\pi/4} \frac{1}{2} \sin(2\phi) \, d\phi = \frac{1}{4} [1 - \cos(\pi/2)].\]This integral becomes: \[\frac{1}{4} [1 - 0] = \frac{1}{4}.\]
05

Integrate with Respect to \( \theta \)

Finally, evaluate the integral with respect to \( \theta \) from 0 to \( 2\pi \):\[\int_{0}^{2\pi} 1 \, d \theta = [\theta]_{0}^{2\pi} = 2\pi.\]
06

Combine Results

Multiply the results of the three integrals to find the value of the triple integral:\[4 \times \frac{1}{4} \times 2\pi = 2\pi.\]

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Key Concepts

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

Triple Integral
A triple integral is a way to integrate over a three-dimensional region. It helps calculate the volume under a surface in three-dimensional space or, as in some physics problems, represents the total amount of some quantity distributed throughout a spatial region. When working with triple integrals, especially in spherical coordinates, you are essentially integrating across a volume defined by certain limits.
Usually, a triple integral is expressed in the form \( \int \int \int \), with each integral representing integration over one of the three dimensions of the space. To solve these integrals, you typically work from inside to outside: first integrating with respect to one variable, then moving on to the next, and finally the third. This structured approach systematically reduces the three-dimensional integral into simpler parts.
In spherical coordinates, these integrals are commonly used to handle volumes that are naturally spherical or involve radial symmetry, such as spheres and cones. This coordinate system is particularly useful because it simplifies the integration process by aligning it with the symmetrical properties of the problem in question.
Integration in Spherical Coordinates
Spherical coordinates are a coordinate system that represents a point in three-dimensional space using three values: the radial distance, the polar angle, and the azimuthal angle. This system is especially useful for functions that involve spheres, such as planetary motion or electromagnetic fields around spherical objects.
When performing integration in spherical coordinates, you transform your integral from Cartesian (x, y, z) to spherical (\(\rho, \phi, \theta\)). The volume element in spherical coordinates is \( \rho^2 \sin \phi \), which accounts for the geometry of spherical shapes. In the exercise, this conversion helps in evaluating volumes or regions that are difficult to express solely in Cartesian terms.
The integration limits typically reflect the bounds of the problem, such as the full range of angles around a sphere or part of it. Learning to read and apply these limits is crucial for evaluating integrals correctly in spherical coordinates.
Polar Angle
The polar angle, often represented as \( \phi \), is one of the angles used in spherical coordinates to describe a location in three-dimensional space. It measures the angle from the positive z-axis downward to the point. In mathematical terms, this angle effectively runs from the 'north pole' of the system to its equator.
Each function or problem in spherical coordinates will specify different limits for \( \phi \), reflecting the part of space it covers. In the given problem, \( \phi \) goes from 0 to \( \pi/4 \), indicating a slice of the sphere that starts straight up and goes down 45 degrees.
This angular measure is vital for defining how far down your slice of spherical volume extends. By manipulating and setting bounds for \( \phi \), you can control which part of a sphere or hemisphere you are considering in your evaluations, enabling accurate volume or region calculation.
Azimuthal Angle
The azimuthal angle, denoted as \( \theta \), acts like the longitude in geographical coordinates. It measures the rotation around the vertical (z-axis), effectively covering the 360-degree span as you circle around the equator of the sphere.
In spherical coordinates, \( \theta \) is crucial for defining the orientation of the object or volume you are working with, as it elongates the planar slice across the horizontal plane of the spherical object. Typical limits for \( \theta \) run from 0 to \( 2\pi \) to cover the full circle around the object, as seen in the given problem.
Understanding the azimuthal angle allows you to capture the entire circumferential aspect of a circular or spherical feature. This angle makes spherical coordinates uniquely suited to rotationally symmetric objects, where the symmetry is about the z-axis, streamlining calculations for volumes that are cumbersome in Cartesian outlines.

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Most popular questions from this chapter

Find the volume of the wedge cut from the first octant by the cylinder \(z=12-3 y^{2}\) and the plane \(x+y=2\)

Find the volume of the solid in the first octant bounded by the coordinate planes, the plane \(x=3,\) and the parabolic cylinder \(z=4-y^{2}\)

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Area formula in polar coordinates Use the double integral in polar coordinates to derive the formula $$A=\int_{\alpha}^{\beta} \frac{1}{2} r^{2} d \theta$$ for the area of the fan-shaped region between the origin and polar curve \(r=f(\theta), \alpha \leq \theta \leq \beta\)

The Parallel Axis Theorem Let \(L_{\mathrm{cm}}\) be a line through the center of mass of a body of mass \(m\) and let \(L\) be a parallel line \(h\) units away from \(L_{c . m .}\) The Parallel Axis Theorem says the moments of inertia \(I_{\mathrm{cm}}\) and \(I_{L}\) of the body about \(L_{\mathrm{cm}}\) and \(L\) satisfy the equation $$ I_{L}=I_{\mathrm{c.m.}}+m h^{2} $$ As in the two-dimensional case, the theorem gives a quick way to calculate one moment when the other moment and the mass are known. Proof of the Parallel Axis Theorem a. Show that the first moment of a body in space about any plane through the body's center of mass is zero. (Hint: Place the body's center of mass at the origin and let the plane be the \(y z\) -plane. What does the formula \(\overline{x}=M_{y z} / M\) then tell you?) b. To prove the Parallel Axis Theorem, place the body with its center of mass at the origin, with the line \(L_{c . m . \text { along the }}\) \(z\) z-axis and the line \(L\) perpendicular to the \(x y\) -plane at the point \((h, 0,0) .\) Let \(D\) be the region of space occupied by the body. Then, in the notation of the figure, $$ I_{L}=\iiint_{D}|\mathbf{v}-h \mathbf{i}|^{2} d m $$ Expand the integrand in this integral and complete the proof.

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