Chapter 6: Problem 8
Find the area of the surface generated when the given curve is revolved about the \(x\) -axis. $$y=x^{3} \text { on }[0,1]$$
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Chapter 6: Problem 8
Find the area of the surface generated when the given curve is revolved about the \(x\) -axis. $$y=x^{3} \text { on }[0,1]$$
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Refer to Exercises 95 and 96. a. Compute a jumper's terminal velocity, which is defined as \(\lim _{t \rightarrow \infty} v(t)=\lim _{t \rightarrow \infty} \sqrt{\frac{m g}{k}} \tanh (\sqrt{\frac{k g}{m}} t)\) b. Find the terminal velocity for the jumper in Exercise 96 \((m=75 \mathrm{kg} \text { and } k=0.2)\) c. How long does it take for any falling object to reach a speed equal to \(95 \%\) of its terminal velocity? Leave your answer in terms of \(k, g,\) and \(m\) d. How tall must a cliff be so that the BASE jumper \((m=75 \mathrm{kg}\) and \(k=0.2\) ) reaches \(95 \%\) of terminal velocity? Assume that the jumper needs at least \(300 \mathrm{m}\) at the end of free fall to deploy the chute and land safely.
When the catenary \(y=a \cosh (x / a)\) is rotated around the \(x\) -axis, it sweeps out a surface of revolution called a catenoid. Find the area of the surface generated when \(y=\cosh x\) on \([-\ln 2, \ln 2]\) is rotated around the \(x\) -axis.
A tsunami is an ocean wave often caused by earthquakes on the ocean floor; these waves typically have long wavelengths, ranging between 150 to \(1000 \mathrm{km}\). Imagine a tsunami traveling across the Pacific Ocean, which is the deepest ocean in the world, with an average depth of about 4000 m. Explain why the shallow-water velocity equation (Exercise 71 ) applies to tsunamis even though the actual depth of the water is large. What does the shallow- water equation say about the speed of a tsunami in the Pacific Ocean (use \(d=4000 \mathrm{m}) ?\)
There are several ways to express the indefinite integral of sech \(x\). a. Show that \(\int \operatorname{sech} x d x=\tan ^{-1}(\sinh x)+C\) (Theorem 9 ). (Hint: Write sech \(x=\frac{1}{\cosh x}=\frac{\cosh x}{\cosh ^{2} x}=\frac{\cosh x}{1+\sinh ^{2} x},\) and then make a change of variables.) b. Show that \(\int \operatorname{sech} x d x=\sin ^{-1}(\tanh x)+C .\) (Hint: Show that sech \(x=\frac{\operatorname{sech}^{2} x}{\sqrt{1-\tanh ^{2} x}}\) and then make a change of variables.) c. Verify that \(\int \operatorname{sech} x d x=2 \tan ^{-1}\left(e^{x}\right)+C\) by proving \(\frac{d}{d x}\left(2 \tan ^{-1}\left(e^{x}\right)\right)=\operatorname{sech} x\).
A large building shaped like a box is 50 \(\mathrm{m}\) high with a face that is \(80 \mathrm{m}\) wide. A strong wind blows directly at the face of the building, exerting a pressure of \(150 \mathrm{N} / \mathrm{m}^{2}\) at the ground and increasing with height according to \(P(y)=150+2 y,\) where \(y\) is the height above the ground. Calculate the total force on the building, which is a measure of the resistance that must be included in the design of the building.
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