Math Problem Statement

Let S be the solid obtained by rotating the region shown in the figure below about the y-axis. y=4sin(2x^2), x=sqrt(pi/2). Use the method of cylindrical shells to find the volume V of S.What are the circumference c and height h of a typical cylindrical shell?

Solution

To solve this problem using the method of cylindrical shells, let's first break it down into the key components and then answer the specific question about the circumference cc and height hh of a typical shell.

Volume of Solid Using Cylindrical Shells:

The formula for the volume VV of a solid of revolution obtained by rotating a region around the y-axis using cylindrical shells is:

V=ab2πxh(x)dxV = \int_{a}^{b} 2\pi x \cdot h(x) \, dx

Where:

  • xx is the radius of the shell (distance from the y-axis),
  • h(x)h(x) is the height of the shell (the function defining the region),
  • 2πx2\pi x is the circumference of the shell,
  • [a,b][a, b] is the interval for xx.

Step 1: Circumference cc

For the method of cylindrical shells, the radius of a typical shell is the xx-coordinate of the point on the curve being rotated. The circumference of the shell is the distance around the shell, given by:

c=2πxc = 2\pi x

Thus, the circumference of a typical cylindrical shell at xx is:

c=2πxc = 2\pi x

Step 2: Height hh

The height of a typical shell is the vertical distance between the curve y=4sin(2x2)y = 4\sin(2x^2) and the x-axis (since we're rotating around the y-axis). Therefore, the height of the shell is simply the value of the function at that point, i.e., h(x)=4sin(2x2)h(x) = 4\sin(2x^2).

So, the height of a typical shell is:

h(x)=4sin(2x2)h(x) = 4\sin(2x^2)

Step 3: Interval of Integration

Since we are given that x=π2x = \sqrt{\frac{\pi}{2}} is the upper limit of xx, the volume integral will be evaluated over the interval [0,π2][0, \sqrt{\frac{\pi}{2}}].

Let me know if you'd like to proceed with calculating the full volume or if you have any questions about these steps.

Here are 5 questions that extend the current problem:

  1. How do you compute the integral of 4sin(2x2)4 \sin(2x^2)?
  2. What happens to the method of cylindrical shells when rotating around an axis other than the y-axis?
  3. Can you use the disk method to solve this problem instead of cylindrical shells?
  4. How do you determine the limits of integration when rotating around the x-axis?
  5. What role does symmetry play in calculating volumes of solids of revolution?

Tip: Always identify the axis of rotation clearly before applying any integration method.

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Math Problem Analysis

Mathematical Concepts

Calculus
Solid of Revolution
Cylindrical Shell Method
Integration

Formulas

V = ∫[a,b] 2πx * h(x) dx
c = 2πx
h(x) = 4sin(2x^2)

Theorems

Method of Cylindrical Shells
Solid of Revolution about the y-axis

Suitable Grade Level

Undergraduate Calculus (Grades 11-12 or higher)