Chapter 12: Problem 66
Use the method of your choice to evaluate the following limits. $$\lim _{(u, v) \rightarrow(-1,0)} \frac{u v e^{-v}}{u^{2}+v^{2}}$$
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Chapter 12: Problem 66
Use the method of your choice to evaluate the following limits. $$\lim _{(u, v) \rightarrow(-1,0)} \frac{u v e^{-v}}{u^{2}+v^{2}}$$
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Potential functions arise frequently in physics and engineering. A potential function has the property that \(a\) field of interest (for example, an electric field, a gravitational field, or a velocity field is the gradient of the potential (or sometimes the negative of the gradient of the potential). (Potential functions are considered in depth in Chapter 14 .) The gravitational potential associated with two objects of mass \(M\) and \(m\) is \(\varphi=-G M m / r,\) where \(G\) is the gravitational constant. If one of the objects is at the origin and the other object is at \(P(x, y, z),\) then \(r^{2}=x^{2}+y^{2}+z^{2}\) is the square of the distance between the objects. The gravitational field at \(P\) is given by \(\mathbf{F}=-\nabla \varphi,\) where \(\nabla \varphi\) is the gradient in three dimensions. Show that the force has a magnitude \(|\mathbf{F}|=G M m / r^{2}\) Explain why this relationship is called an inverse square law.
Suppose you follow the spiral path \(C: x=\cos t, y\) \(=\sin t, z=\) \(t,\) for \(t \geq 0,\) through the domain of the function \(w=f(x, y, z)=x y z /\left(z^{2}+1\right)\) a. Find \(w^{\prime}(t)\) along \(C\) b. Estimate the point \((x, y, z)\) on \(C\) at which \(w\) has its maximum value.
Determine whether the following statements are true and give an explanation or counterexample. a. Suppose you are standing at the center of a sphere looking at a point \(P\) on the surface of the sphere. Your line of sight to \(P\) is orthogonal to the plane tangent to the sphere at \(P\). b. At a point that maximizes \(f\) on the curve \(g(x, y)=0,\) the dot product \(\nabla f \cdot \nabla g\) is zero.
The equation \(x^{2 n}+y^{2 n}+z^{2 n}=1,\) where \(n\) is a positive integer, describes a flattened sphere. Define the extreme points to be the points on the flattened sphere with a maximum distance from the origin. a. Find all the extreme points on the flattened sphere with \(n=2\) What is the distance between the extreme points and the origin? b. Find all the extreme points on the flattened sphere for integers \(n>2 .\) What is the distance between the extreme points and the origin? c. Give the location of the extreme points in the limit as \(n \rightarrow \infty\). What is the limiting distance between the extreme points and the origin as \(n \rightarrow \infty ?\)
Consider the curve \(\mathbf{r}(t)=\langle\cos t, \sin t, c \sin t\rangle\) for \(0 \leq t \leq 2 \pi,\) where \(c\) is a real number. a. What is the equation of the plane \(P\) in which the curve lies? b. What is the angle between \(P\) and the \(x y\) -plane? c. Prove that the curve is an ellipse in \(P\).
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