Math Problem Statement

Determine the volume of the solid generated by rotating the first quadrant region of 𝑦 = π‘₯ ! βˆ’ 2, bounded by 𝑦 = 0 and π‘₯ = 2, about the y-axis. Use method of disks

Solution

To find the volume of the solid generated by rotating the region bounded by y=x3βˆ’2y = x^3 - 2, y=0y = 0, and x=2x = 2 about the y-axis using the method of disks, we will follow these steps:

Step 1: Express the equation in terms of xx

The equation y=x3βˆ’2y = x^3 - 2 is already in terms of xx. We can solve for xx as a function of yy since we are rotating about the y-axis. To do this:

y=x3βˆ’2β€…β€ŠβŸΉβ€…β€Šx3=y+2β€…β€ŠβŸΉβ€…β€Šx=y+23y = x^3 - 2 \implies x^3 = y + 2 \implies x = \sqrt[3]{y + 2}

Step 2: Setup the integral

When using the method of disks (or washers) for rotation about the y-axis, the volume of the solid is given by the formula:

V=Ο€βˆ«y1y2[f(y)2]dyV = \pi \int_{y_1}^{y_2} \left[ f(y)^2 \right] dy

Where f(y)f(y) is the radius of the solid at a given point yy, and y1y_1 and y2y_2 are the bounds for yy. The function f(y)f(y) represents the distance from the y-axis to the curve, which in this case is f(y)=y+23f(y) = \sqrt[3]{y + 2}.

Step 3: Determine the limits of integration

  • The region of interest is bounded by x=0x = 0 (the y-axis) and x=2x = 2, and the equation is given by y=x3βˆ’2y = x^3 - 2.
  • At x=0x = 0, y=03βˆ’2=βˆ’2y = 0^3 - 2 = -2.
  • At x=2x = 2, y=23βˆ’2=8βˆ’2=6y = 2^3 - 2 = 8 - 2 = 6.

So, the limits of integration are from y=βˆ’2y = -2 to y=6y = 6.

Step 4: Volume Integral

Now we can write the volume integral:

V=Ο€βˆ«βˆ’26(y+23)2dyV = \pi \int_{-2}^{6} \left( \sqrt[3]{y + 2} \right)^2 dy

This simplifies to:

V=Ο€βˆ«βˆ’26(y+2)2/3 dyV = \pi \int_{-2}^{6} (y + 2)^{2/3} \, dy

Step 5: Solve the Integral

To solve the integral, we can use the power rule for integration:

∫(y+2)2/3 dy=35(y+2)5/3+C\int (y + 2)^{2/3} \, dy = \frac{3}{5} (y + 2)^{5/3} + C

Now, apply the limits of integration:

V=Ο€[35(y+2)5/3]βˆ’26V = \pi \left[ \frac{3}{5} (y + 2)^{5/3} \right]_{-2}^{6}

Substituting the limits:

V=Ο€[35(6+2)5/3βˆ’35(βˆ’2+2)5/3]V = \pi \left[ \frac{3}{5} (6 + 2)^{5/3} - \frac{3}{5} (-2 + 2)^{5/3} \right] V=Ο€[35(8)5/3βˆ’35(0)5/3]V = \pi \left[ \frac{3}{5} (8)^{5/3} - \frac{3}{5} (0)^{5/3} \right] V=Ο€[35Γ—32]V = \pi \left[ \frac{3}{5} \times 32 \right] V=π×965V = \pi \times \frac{96}{5}

Thus, the volume of the solid is:

V=96Ο€5V = \frac{96\pi}{5}

Final Answer:

V=96Ο€5 cubic units.V = \frac{96\pi}{5} \, \text{cubic units}.

Would you like further explanation or details on any step?


Related questions to explore:

  1. How would the volume change if the region were rotated about the x-axis?
  2. What is the volume of the solid generated by rotating y=x2y = x^2 about the y-axis from x=0x = 0 to x=3x = 3?
  3. What happens to the volume if the region is bounded by different curves or limits?
  4. How does the disk method compare to the washer method in terms of application?
  5. Can you use the shell method to solve for the volume of the same solid?

Tip: When performing integrals with fractional exponents, always double-check the algebra for any potential mistakes when simplifying powers, as they can be tricky.

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Math Problem Analysis

Mathematical Concepts

Calculus
Integral Calculus
Volume of Solids of Revolution
Disk Method

Formulas

Volume formula using the disk method: V = Ο€ ∫[y1 to y2] [f(y)]^2 dy
Function transformation: x = (y + 2)^(1/3)
Integral formula: ∫ (y + a)^n dy = (1/(n+1)) (y + a)^(n+1) + C

Theorems

Disk Method for Volume Calculation
Power Rule for Integration

Suitable Grade Level

Undergraduate Calculus (College Level) / Advanced High School (AP Calculus BC)