Chapter 6 Review Excercises
True or False? Justify your answer with a proof or a counterexample.1. The amount of work to pump the water out of a half-full cylinder is half the amount of work to pump the water out of the full cylinder.
Answer:
False
2. If the force is constant, the amount of work to move an object from [latex]x=a[/latex] to [latex]x=b[/latex] is [latex]F(b-a).[/latex]
3. The disk method can be used in any situation in which the washer method is successful at finding the volume of a solid of revolution.
Answer:
False
4. If the half-life of [latex]\text{seaborgium-}266[/latex] is 360 ms, then [latex]k=(\text{ln}(2))\text{/}360.[/latex]
For the following exercises, use the requested method to determine the volume of the solid.
5. The volume that has a base of the ellipse [latex]{x}^{2}\text{/}4+{y}^{2}\text{/}9=1[/latex] and cross-sections of an equilateral triangle perpendicular to the [latex]y\text{-axis}\text{.}[/latex] Use the method of slicing.
Answer:
[latex]32\sqrt{3}[/latex]
6. [latex]y={x}^{2}-x,[/latex] from [latex]x=1\text{ to }x=4,[/latex] rotated around the[latex]y[/latex]-axis using the washer method
7. [latex]x={y}^{2}[/latex] and [latex]x=3y[/latex] rotated around the [latex]y[/latex]-axis using the washer method
Answer:
[latex]\frac{162\pi }{5}[/latex]
8. [latex]x=2{y}^{2}-{y}^{3},x=0,\text{ and }y=0[/latex] rotated around the [latex]x[/latex]-axis using cylindrical shells
For the following exercises, find
- the area of the region,
- the volume of the solid when rotated around the [latex]x[/latex]-axis, and
- the volume of the solid when rotated around the [latex]y[/latex]-axis. Use whichever method seems most appropriate to you.
9. [latex]y={x}^{3},x=0,y=0,\text{ and }x=2[/latex]
Answer:
a. 4, b. [latex]\frac{128\pi }{7},[/latex] c. [latex]\frac{64\pi }{5}[/latex]
11. [T][latex]y=\text{ln}(x)+2\text{ and }y=x[/latex]
Answer:
a. 1.949, b. 21.952, c. 17.099
12. [latex]y={x}^{2}[/latex] and [latex]y=\sqrt{x}[/latex]
13. [latex]y=5+x,[/latex][latex]y={x}^{2},[/latex][latex]x=0,[/latex] and [latex]x=1[/latex]
Answer:
a. [latex]\frac{31}{6},[/latex] b. [latex]\frac{452\pi }{15},[/latex] c. [latex]\frac{31\pi }{6}[/latex]
14. Below [latex]{x}^{2}+{y}^{2}=1[/latex] and above [latex]y=1-x[/latex]
15. Find the mass of [latex]\rho ={e}^{\text{−}x}[/latex] on a disk centered at the origin with radius 4.
Answer:
245.282
16. Find the center of mass for [latex]\rho ={ \tan }^{2}x[/latex] on [latex]x\in (-\frac{\pi }{4},\frac{\pi }{4}).[/latex]
17. Find the mass and the center of mass of [latex]\rho =1[/latex] on the region bounded by [latex]y={x}^{5}[/latex] and [latex]y=\sqrt{x}.[/latex]
Answer:
Mass: [latex]\frac{1}{2},[/latex] center of mass: [latex](\frac{18}{35},\frac{9}{11})[/latex]
For the following exercises, find the requested arc lengths.
18. The length of [latex]x[/latex] for [latex]y=\text{cosh}(x)[/latex] from [latex]x=0\text{ to }x=2.[/latex]
19. The length of [latex]y[/latex] for [latex]x=3-\sqrt{y}[/latex] from [latex]y=0[/latex] to [latex]y=4[/latex]
Answer:
[latex]\sqrt{17}+\frac{1}{8}\text{ln}(33+8\sqrt{17})[/latex]
For the following exercises, find the surface area and volume when the given curves are revolved around the specified axis.
21. The loudspeaker created by revolving [latex]y=1\text{/}x[/latex] from [latex]x=1[/latex] to [latex]x=4[/latex] around the [latex]x[/latex]-axis.
Answer:
Volume: [latex]\frac{3\pi }{4},[/latex] surface area: [latex]\pi (\sqrt{2}-{\text{sinh}}^{-1}(1)+{\text{sinh}}^{-1}(16)-\frac{\sqrt{257}}{16})[/latex]
For the following exercises, consider the Karun-3 dam in Iran. Its shape can be approximated as an isosceles triangle with height 205 m and width 388 m. Assume the current depth of the water is 180 m. The density of water is 1000 kg/m [latex]{}^{3}.[/latex]
22. Find the total force on the wall of the dam.
23. You are a crime scene investigator attempting to determine the time of death of a victim. It is noon and [latex]45\text{°}\text{F}[/latex] outside and the temperature of the body is [latex]78\text{°}\text{F}.[/latex] You know the cooling constant is [latex]k=0.00824\text{°}\text{F/min}\text{.}[/latex] When did the victim die, assuming that a human’s temperature is [latex]98\text{°}\text{F}[/latex] ?
Answer:
11:02 a.m.
For the following exercise, consider the stock market crash in 1929 in the United States. The table lists the Dow Jones industrial average per year leading up to the crash.
| Years after 1920 | Value ($) |
|---|---|
| 1 | 63.90 |
| 3 | 100 |
| 5 | 110 |
| 7 | 160 |
| 9 | 381.17 |
For the following exercises, consider the catenoid, the only solid of revolution that has a minimal surface, or zero mean curvature. A catenoid in nature can be found when stretching soap between two rings.
25. Find the volume of the catenoid [latex]y=\text{cosh}(x)[/latex] from [latex]x=-1\text{ to }x=1[/latex] that is created by rotating this curve around the [latex]x\text{-axis},[/latex] as shown here.
Answer:
[latex]\pi (1+\text{sinh}(1)\text{cosh}(1))[/latex]
26. Find surface area of the catenoid [latex]y=\text{cosh}(x)[/latex] from [latex]x=-1[/latex] to [latex]x=1[/latex] that is created by rotating this curve around the [latex]x\text{-axis.}[/latex]
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