Math Problem Statement

A solid lies between planes perpendicular to the y-axis at y = 0 and y = 2. The cross-sections perpendicular to the y-axis are circular disks with diameters running from the y-axis to the parabola x = sqrt(17)y^2. Find the volume of the solid.

Solution

The problem describes a solid between planes perpendicular to the yy-axis at y=0y = 0 and y=2y = 2. The cross-sections of the solid are circular disks whose diameters run from the yy-axis to the curve given by the equation x=17y2x = \sqrt{17}y^2.

Steps to solve:

  1. Understanding the cross-sections: The cross-sections perpendicular to the yy-axis are circular disks. The diameter of each disk at a given value of yy runs from the yy-axis (x=0x = 0) to the curve x=17y2x = \sqrt{17}y^2. So, the diameter of the disk at any yy is: Diameter=17y20=17y2.\text{Diameter} = \sqrt{17}y^2 - 0 = \sqrt{17}y^2. The radius of the disk is half the diameter, so the radius is: Radius=17y22.\text{Radius} = \frac{\sqrt{17}y^2}{2}.

  2. Area of a circular cross-section: The area A(y)A(y) of a circular cross-section at a given yy is given by the formula for the area of a circle A=πr2A = \pi r^2. Substituting the radius: A(y)=π(17y22)2=π17y44.A(y) = \pi \left( \frac{\sqrt{17}y^2}{2} \right)^2 = \pi \cdot \frac{17y^4}{4}.

  3. Volume of the solid: The volume of the solid can be found by integrating the area of the cross-sections along the yy-axis from y=0y = 0 to y=2y = 2: V=02A(y)dy=02π17y44dy.V = \int_0^2 A(y) \, dy = \int_0^2 \pi \cdot \frac{17y^4}{4} \, dy. Simplifying the integral: V=17π402y4dy.V = \frac{17\pi}{4} \int_0^2 y^4 \, dy. Now, compute the integral of y4y^4: y4dy=y55.\int y^4 \, dy = \frac{y^5}{5}. Evaluating this from y=0y = 0 to y=2y = 2: 02y4dy=(2)55(0)55=325.\int_0^2 y^4 \, dy = \frac{(2)^5}{5} - \frac{(0)^5}{5} = \frac{32}{5}.

  4. Final volume: Substituting this back into the expression for the volume: V=17π4×325=17×32×π20=544π20=27.2π.V = \frac{17\pi}{4} \times \frac{32}{5} = \frac{17 \times 32 \times \pi}{20} = \frac{544\pi}{20} = 27.2\pi.

Thus, the volume of the solid is 27.2π27.2\pi cubic units.

Would you like further details or explanations on any part of the solution?

Here are 5 related questions for practice:

  1. How would the volume change if the parabola equation was x=10y2x = \sqrt{10}y^2?
  2. What if the cross-sections were squares instead of circular disks?
  3. How can you use cylindrical coordinates to solve a problem with circular cross-sections?
  4. What is the physical interpretation of cross-sectional volumes in real-world applications?
  5. How would the limits of integration change if the region extended to y=4y = 4?

Tip: Always check the units of the result, especially in physical applications where the dimensions of objects must match!

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Math Problem Analysis

Mathematical Concepts

Solid Geometry
Cross-sectional Area
Integration

Formulas

Area of a circle: A = πr^2
Volume by integration: V = ∫ A(y) dy
Equation of parabola: x = sqrt(17)y^2

Theorems

Method of Disk Integration

Suitable Grade Level

Grade 12 / College Level Calculus