/*! 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 42 Find the average value of the te... [FREE SOLUTION] | 91Ó°ÊÓ

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Find the average value of the temperature function \(T(x, y, z)=100-25 z\) on the cone \(z^{2}=x^{2}+y^{2},\) for \(0 \leq z \leq 2\)

Short Answer

Expert verified
Answer: The average value of the temperature function on the cone is 100.

Step by step solution

01

Finding the volume of the cone

Firstly, let's find the volume of the cone using triple integral in spherical coordinates. Converting \(z^2 = x^2 + y^2\) into cylindrical coordinates, we get: $$\rho^2 = z^2$$ Here, \(0 \leq \rho \leq z\), \(0 \leq \theta \leq 2\pi\), and \(0\leq z\leq 2\). Therefore, the volume of the cone, \(V\), in terms of cylindrical coordinates is given by: $$V = \int\limits_0^2 \int\limits_0^{2\pi} \int\limits_0^z \rho\, \text{d}\rho\, \text{d}\theta\, \text{d}z$$ Now let's evaluate the integral: $$ V = \int\limits_0^2\int\limits_0^{2\pi}\frac{z^3}{2}\text{d}\theta \text{d}z $$ $$ V = \int\limits_0^2 z^3 \left[\int\limits_0^{2\pi}\text{d}\theta\right] \text{d}z $$ $$ V = \int_0^2 z^3 (2\pi) \text{d}z $$ $$ V= 2\pi\left[\frac{z^4}{4}\right]_0^2 $$ $$ V = 2\pi\left(4\right)=8\pi $$ The volume of the cone is \(V = 8\pi\).
02

Evaluate the integral of T(x, y, z) over the cone

Using cylindrical coordinates for the triple integral, we get: $$\int\limits_0^2 \int\limits_0^{2\pi} \int\limits_0^z (100 - 25z) \rho\, \text{d}\rho\, \text{d}\theta\, \text{d}z$$ Let's evaluate the integral: $$ \int\limits_0^2\int\limits_0^{2\pi}\frac{(100 - 25z) z^3}{2}\text{d}\theta \text{d}z $$ $$ \int\limits_0^2(100 - 25z) z^3\left[\int\limits_0^{2\pi}\text{d}\theta\right] \text{d}z $$ $$ \int\limits_0^2 (100 - 25z) z^3 (2\pi) \text{d}z $$ $$ 2\pi\left[\int\limits_0^2 (100z^3 - 25z^4) \text{d}z\right] $$ $$ 2\pi\left[\frac{100z^4}{4} - \frac{25z^5}{5}\right]_0^2 $$ The result of the integral is \(800\pi\).
03

Calculate the average value of T(x, y, z)

Now divide the result of the integral with the volume of the cone: $$ \text{Average value} = \frac{800\pi}{8\pi} $$ $$ \text{Average value} = 100 $$ The average value of the temperature function \(T(x, y, z) = 100 - 25z\) on the cone \(z^2 = x^2 + y^2\) for \(0 \leq z \leq 2\) is 100.

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Most popular questions from this chapter

A beautiful flux integral Consider the potential function \(\varphi(x, y, z)=G(\rho),\) where \(G\) is any twice differentiable function and \(\rho=\sqrt{x^{2}+y^{2}+z^{2}} ;\) therefore, \(G\) depends only on the distance from the origin. a. Show that the gradient vector field associated with \(\varphi\) is \(\mathbf{F}=\nabla \varphi=G^{\prime}(\rho) \frac{\mathbf{r}}{\rho},\) where \(\mathbf{r}=\langle x, y, z\rangle\) and \(\rho=|\mathbf{r}|\)b. Let \(S\) be the sphere of radius \(a\) centered at the origin and let \(D\) be the region enclosed by \(S\). Show that the flux of \(\mathbf{F}\) across \(S\) is \(\iint_{S} \mathbf{F} \cdot \mathbf{n} d S=4 \pi a^{2} G^{\prime}(a)\) c. Show that \(\nabla \cdot \mathbf{F}=\nabla \cdot \nabla \varphi=\frac{2 G^{\prime}(\rho)}{\rho}+G^{\prime \prime}(\rho)\) d. Use part (c) to show that the flux across \(S\) (as given in part (b)) is also obtained by the volume integral \(\iiint_{D} \nabla \cdot \mathbf{F} d V\) (Hint: Use spherical coordinates and integrate by parts.)

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