Chapter 14: Problem 1
Explain how to compute the divergence of the vector field \(\mathbf{F}=\langle f, g, h\rangle\).
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Chapter 14: Problem 1
Explain how to compute the divergence of the vector field \(\mathbf{F}=\langle f, g, h\rangle\).
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Prove the following properties of the divergence and curl. Assume \(\mathbf{F}\) and \(\mathbf{G}\) are differentiable vector fields and \(c\) is a real number. a. \(\nabla \cdot(\mathbf{F}+\mathbf{G})=\nabla \cdot \mathbf{F}+\nabla \cdot \mathbf{G}\) b. \(\nabla \times(\mathbf{F}+\mathbf{G})=(\nabla \times \mathbf{F})+(\nabla \times \mathbf{G})\) c. \(\nabla \cdot(c \mathbf{F})=c(\nabla \cdot \mathbf{F})\) d. \(\nabla \times(c \mathbf{F})=c(\nabla \times \mathbf{F})\)
Let \(\mathbf{F}=\langle z, 0,0\rangle\) and let \(\mathbf{n}\) be a unit vector aligned with the axis of a paddle wheel located on the \(x\) -axis (see figure). a. If the paddle wheel is oriented with \(\mathbf{n}=\langle 1,0,0\rangle,\) in what direction (if any) does the wheel spin? b. If the paddle wheel is oriented with \(\mathbf{n}=\langle 0,1,0\rangle,\) in what direction (if any) does the wheel spin? c. If the paddle wheel is oriented with \(\mathbf{n}=\langle 0,0,1\rangle,\) in what direction (if any) does the wheel spin?
The area of a region \(R\) in the plane, whose boundary is the closed curve \(C,\) may be computed using line integrals with the formula $$\text { area of } R=\int_{C} x d y=-\int_{C} y d x$$ These ideas reappear later in the chapter. Let \(R\) be the rectangle with vertices \((0,0),(a, 0),(0, b),\) and \((a, b),\) and let \(C\) be the boundary of \(R\) oriented counterclockwise. Use the formula \(A=\int_{C} x d y\) to verify that the area of the rectangle is \(a b.\)
For the general rotation field \(\mathbf{F}=\mathbf{a} \times \mathbf{r},\) where \(\mathbf{a}\) is a nonzero constant vector and \(\mathbf{r}=\langle x, y, z\rangle,\) show that curl \(\mathbf{F}=2 \mathbf{a}\).
Prove that for a real number \(p,\) with \(\mathbf{r}=\langle x, y, z\rangle, \nabla\left(\frac{1}{|\mathbf{r}|^{p}}\right)=\frac{-p \mathbf{r}}{|\mathbf{r}|^{p+2}}.\)
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