Chapter 14: Problem 58
Find the general formula for the surface area of a cone with height \(h\) and base radius \(a\) (excluding the base).
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Chapter 14: Problem 58
Find the general formula for the surface area of a cone with height \(h\) and base radius \(a\) (excluding the base).
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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.)
Let \(S\) be the paraboloid \(z=a\left(1-x^{2}-y^{2}\right),\) for \(z \geq 0,\) where \(a>0\) is a real number. Let \(\mathbf{F}=\langle x-y, y+z, z-x\rangle .\) For what value(s) of \(a\) (if any) does \(\iint_{S}(\nabla \times \mathbf{F}) \cdot \mathbf{n} d S\) have its maximum value?
For the following velocity fields, compute the curl, make a sketch of the curl, and interpret the curl. $$\mathbf{v}=\langle-2 z, 0,1\rangle$$
Consider the radial field \(\mathbf{F}=\frac{\mathbf{r}}{|\mathbf{r}|^{p}}=\frac{\langle x, y, z\rangle}{|\mathbf{r}|^{p}},\) where \(p>1\) (the inverse square law corresponds to \(p=3\) ). Let \(C\) be the line from (1,1,1) to \((a, a, a),\) where \(a>1,\) given by \(\mathbf{r}(t)=\langle t, t, t\rangle,\) for \(1 \leq t \leq a\) a. Find the work done in moving an object along \(C\) with \(p=2\) b. If \(a \rightarrow \infty\) in part (a), is the work finite? c. Find the work done in moving an object moving along \(C\) with \(p=4.\) d. If \(a \rightarrow \infty\) in part (c), is the work finite? e. Find the work done in moving an object moving along \(C\) for any \(p>1\) f. If \(a \rightarrow \infty\) in part (e), for what values of \(p\) is the work finite?
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