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 lying between two planes perpendicular to the yy-axis, specifically at y=0y = 0 and y=1y = 1. The cross-sections perpendicular to the yy-axis are circular disks, and the diameter of these disks runs from the yy-axis to the parabola x=3y2x = \sqrt{3y^2}.

Step-by-step solution:

  1. Interpret the diameter of the circular disks:
    The diameter of each disk at a point yy is the distance from x=0x = 0 (the yy-axis) to the curve x=3y2x = \sqrt{3y^2}. This simplifies to x=3yx = \sqrt{3}y.

    Therefore, the diameter of each circular cross-section is: D(y)=3yD(y) = \sqrt{3}y

  2. Find the radius of the disk:
    The radius r(y)r(y) of the circular disk is half of the diameter: r(y)=D(y)2=3y2r(y) = \frac{D(y)}{2} = \frac{\sqrt{3}y}{2}

  3. Find the area of each cross-section:
    The area A(y)A(y) of a circular cross-section is given by the formula for the area of a circle: A(y)=π(r(y))2=π(3y2)2=π3y24A(y) = \pi \left( r(y) \right)^2 = \pi \left( \frac{\sqrt{3}y}{2} \right)^2 = \pi \frac{3y^2}{4}

  4. Set up the integral for the volume:
    The volume of the solid can be found by integrating the area of the cross-sections from y=0y = 0 to y=1y = 1: V=01A(y)dy=01π3y24dyV = \int_0^1 A(y) \, dy = \int_0^1 \pi \frac{3y^2}{4} \, dy

  5. Evaluate the integral: V=3π401y2dyV = \frac{3\pi}{4} \int_0^1 y^2 \, dy The integral of y2y^2 is: y2dy=y33\int y^2 \, dy = \frac{y^3}{3} Evaluating this from 0 to 1: V=3π4[133033]=3π4×13=π4V = \frac{3\pi}{4} \left[ \frac{1^3}{3} - \frac{0^3}{3} \right] = \frac{3\pi}{4} \times \frac{1}{3} = \frac{\pi}{4}

Final Answer:

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

Would you like any details or have any other questions about this solution?

Here are 5 related questions to further your understanding:

  1. How do we set up integrals for volumes of solids with known cross-sectional areas?
  2. Why is the radius of the disk half of the diameter in this problem?
  3. How does changing the shape of the cross-section affect the volume integral?
  4. What if the parabola was a different function, like x=y2x = y^2? How would that affect the volume?
  5. Could we solve this problem using cylindrical shells instead of cross-sectional disks?

Tip: When dealing with volume integrals, always start by identifying the shape of the cross-sections and express their area as a function of the axis of integration.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Solids of Revolution
Area of Cross-Sections

Formulas

Volume of Solid = ∫ A(y) dy
Area of Circle = πr^2
r(y) = D(y)/2

Theorems

Volume by Slices (Disk Method)

Suitable Grade Level

Undergraduate Calculus