Math Problem Statement

A solid lies between planes perpendicular to the y-axis at y = 0 and y = 1. The cross-sections perpendicular to the y-axis are circular disks with diameters running from the y-axis to the parabola x = √3y^2. Find the volume of the solid.

Solution

The problem describes a solid bounded by planes perpendicular to the yy-axis at y=0y = 0 and y=1y = 1. The cross-sections perpendicular to the yy-axis are circular disks, with diameters running from the yy-axis to the parabola x=3y2x = \sqrt{3y^2}.

Step-by-Step Approach:

  1. Understanding the Cross-Sectional Area: The cross-sections are circular disks, where the diameter extends from the yy-axis (x=0x = 0) to the curve defined by x=3y2x = \sqrt{3y^2}.

    Therefore, the radius rr of each disk at a given yy is half the length of the diameter: r=diameter2=3y22=3y2r = \frac{\text{diameter}}{2} = \frac{\sqrt{3y^2}}{2} = \frac{\sqrt{3} y}{2}

  2. Area of a Disk: The area A(y)A(y) of a circular cross-section is given by: A(y)=πr2=π(3y2)2=π×3y24=3πy24A(y) = \pi r^2 = \pi \left( \frac{\sqrt{3} y}{2} \right)^2 = \pi \times \frac{3y^2}{4} = \frac{3\pi y^2}{4}

  3. Volume of the Solid: To find the volume, we integrate the area of the cross-sections from y=0y = 0 to y=1y = 1: V=01A(y)dy=013πy24dyV = \int_0^1 A(y) \, dy = \int_0^1 \frac{3\pi y^2}{4} \, dy

  4. Calculating the Integral: Now, solve the integral: V=3π401y2dy=3π4[y33]01V = \frac{3\pi}{4} \int_0^1 y^2 \, dy = \frac{3\pi}{4} \left[ \frac{y^3}{3} \right]_0^1 V=3π4×13033=3π4×13=π4V = \frac{3\pi}{4} \times \frac{1^3 - 0^3}{3} = \frac{3\pi}{4} \times \frac{1}{3} = \frac{\pi}{4}

Final Answer:

The volume of the solid is π4\frac{\pi}{4}.


Would you like further details or have any questions?

Here are 5 related questions to expand this concept:

  1. How would the volume change if the diameter ran from x=3y2x = -\sqrt{3y^2} to x=3y2x = \sqrt{3y^2}?
  2. What happens to the volume if the parabola is changed to x=2y2x = \sqrt{2y^2}?
  3. How would you find the volume if the shape was a square instead of a circular disk?
  4. What is the physical significance of such solids in real-world applications?
  5. How does the method change if the parabola is rotated or tilted?

Tip: When integrating for volume, always ensure that the limits of integration and cross-sectional area are correctly defined based on the given geometry.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Volumes of Solids of Revolution
Area of Circular Disks

Formulas

Radius of disk: r = (√3 * y) / 2
Area of a circle: A(y) = πr^2
Volume integral: V = ∫ A(y) dy

Theorems

Disk Method for Volumes

Suitable Grade Level

Grades 11-12 (Advanced Placement Calculus)