Chapter 14: Problem 1
How is a vector field \(\mathbf{F}=\langle f, g, h\rangle\) used to describe the motion of air at one instant in time?
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Chapter 14: Problem 1
How is a vector field \(\mathbf{F}=\langle f, g, h\rangle\) used to describe the motion of air at one instant in time?
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Evaluate each line integral using a method of your choice. $$\begin{aligned} &\oint_{C} \mathbf{F} \cdot d \mathbf{r}, \text { where } \mathbf{F}=\left\langle 2 x y+z^{2}, x^{2}, 2 x z\right\rangle \text { and } C \text { is the circle }\\\ &\mathbf{r}(t)=\langle 3 \cos t, 4 \cos t, 5 \sin t\rangle, \text { for } 0 \leq t \leq 2 \pi \end{aligned}$$
Generalize Exercise 43 to show that the rotation field \(\mathbf{F}=\mathbf{a} \times \mathbf{r}\) circles the vector a in the counterclockwise direction looking along a from head to tail.
Let S be the disk enclosed by the curve \(C: \mathbf{r}(t)=\langle\cos \varphi \cos t, \sin t, \sin \varphi \cos t\rangle,\)for \(0 \leq t \leq 2 \pi,\) where \(0 \leq \varphi \leq \pi / 2\) is a fixed angle. What is the circulation on \(C\) of the vector field \(\mathbf{F}=\langle-y,-z, x\rangle\) as a function of \(\varphi ?\) For what value of \(\varphi\) is the circulation a maximum?
Begin with the paraboloid \(z=x^{2}+y^{2},\) for \(0 \leq z \leq 4,\) and slice it with the plane \(y=0\) Let \(S\) be the surface that remains for \(y \geq 0\) (including the planar surface in the \(x z\) -plane) (see figure). Let \(C\) be the semicircle and line segment that bound the cap of \(S\) in the plane \(z=4\) with counterclockwise orientation. Let \(\mathbf{F}=\langle 2 z+y, 2 x+z, 2 y+x\rangle\) a. Describe the direction of the vectors normal to the surface that are consistent with the orientation of \(C\). b. Evaluate \(\iint_{S}(\nabla \times \mathbf{F}) \cdot \mathbf{n} d S\) c. Evaluate \(\oint_{C} \mathbf{F} \cdot d \mathbf{r}\) and check for agreement with part (b).
\(\mathbb{R}^{2}\) Assume that the vector field \(\mathbf{F}\) is conservative in \(\mathbb{R}^{2}\), so that the line integral \(\int_{C} \mathbf{F} \cdot d \mathbf{r}\) is independent of path. Use the following procedure to construct a potential function \(\varphi\) for the vector field \(\mathbf{F}=\langle f, g\rangle=\langle 2 x-y,-x+2 y\rangle\) a. Let \(A\) be (0,0) and let \(B\) be an arbitrary point \((x, y) .\) Define \(\varphi(x, y)\) to be the work required to move an object from \(A\) to \(B\) where \(\varphi(A)=0 .\) Let \(C_{1}\) be the path from \(A\) to \((x, 0)\) to \(B\) and let \(C_{2}\) be the path from \(A\) to \((0, y)\) to \(B .\) Draw a picture. b. Evaluate \(\int_{C_{1}} \mathbf{F} \cdot d \mathbf{r}=\int_{C_{1}} f d x+g d y\) and conclude that \(\varphi(x, y)=x^{2}-x y+y^{2}\) c. Verify that the same potential function is obtained by evaluating the line integral over \(C_{2}\)
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