Chapter 14: Problem 49
For what vectors \(\mathbf{n}\) is \((\operatorname{curl} \mathbf{F}) \cdot \mathbf{n}=0\) when \(\mathbf{F}=\langle y,-2 z,-x\rangle ?\)
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Chapter 14: Problem 49
For what vectors \(\mathbf{n}\) is \((\operatorname{curl} \mathbf{F}) \cdot \mathbf{n}=0\) when \(\mathbf{F}=\langle y,-2 z,-x\rangle ?\)
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Consider the radial vector fields \(\mathbf{F}=\mathbf{r} /|\mathbf{r}|^{p},\) where \(p\) is a real number and \(\mathbf{r}=\langle x, y, z\rangle\) Let \(C\) be any circle in the \(x y\) -plane centered at the origin. a. Evaluate a line integral to show that the field has zero circulation on \(C\) b. For what values of \(p\) does Stokes' Theorem apply? For those values of \(p,\) use the surface integral in Stokes' Theorem to show that the field has zero circulation on \(C\).
Prove that if \(\mathbf{F}\) satisfies the conditions of Stokes' Theorem, then \(\iint_{S}(\nabla \times \mathbf{F}) \cdot \mathbf{n} d S=0\) where \(S\) is a smooth surface that encloses a region.
Use the procedure in Exercise 57 to construct potential functions for the following fields. $$\mathbf{F}=\langle-y,-x\rangle$$
The potential function for the gravitational force field due to a mass \(M\) at the origin acting on a mass \(m\) is \(\varphi=G M m /|\mathbf{r}|,\) where \(\mathbf{r}=\langle x, y, z\rangle\) is the position vector of the mass \(m\) and \(G\) is the gravitational constant. a. Compute the gravitational force field \(\mathbf{F}=-\nabla \varphi\). b. Show that the field is irrotational; that is, \(\nabla \times \mathbf{F}=\mathbf{0}\).
Consider the radial field \(\mathbf{F}=\mathbf{r} /|\mathbf{r}|^{p}\) where \(\mathbf{r}=\langle x, y, z\rangle\) and \(p\) is a real number. Let \(S\) be the sphere of radius \(a\) centered at the origin. Show that the outward flux of \(\mathbf{F}\) across the sphere is \(4 \pi / a^{p-3} .\) It is instructive to do the calculation using both an explicit and parametric description of the sphere.
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