Math Problem Statement

Dengan metode kulit tabung, tentukan volume benda putar dari daerah yang dibatasi sumbu y, garis y=2, dan kurva x=y^2 jika diputar terhadap garis y=0!

Solution

To solve the problem, we need to calculate the volume of the solid of revolution using the shell method (metode kulit tabung). Here's how we analyze the situation:

Problem Breakdown:

  1. The region is bounded by:

    • x=y2x = y^2: a parabola opening to the right.
    • y=2y = 2: a horizontal line.
    • The solid is rotated around the line y=0y = 0.
  2. Shell Method Formula: V=ab2π(radius)(height)dyV = \int_{a}^{b} 2\pi (\text{radius})(\text{height}) \, dy

    • Radius: The distance from the axis of rotation y=0y = 0 is simply yy.
    • Height: The height of the shell is the horizontal length of the region, which is: Height=4y2\text{Height} = 4 - y^2 (from the right boundary x=4x = 4 minus x=y2x = y^2).
  3. Limits of Integration: The region extends vertically from y=0y = 0 to y=2y = 2.

Substituting Values:

V=022π(y)(4y2)dyV = \int_{0}^{2} 2\pi (y)(4 - y^2) \, dy

Simplification:

Expanding the integral: V=022π(4yy3)dyV = \int_{0}^{2} 2\pi \big( 4y - y^3 \big) \, dy This matches Option (e): V=022πy(4y2)dyV = \int_{0}^{2} 2\pi y (4 - y^2) \, dy

Correct Answer:

The correct answer is Option (e).


Let me know if you'd like further explanation or detailed steps for integration! Here are five related questions for practice:

  1. What is the volume of a solid of revolution if the same region is rotated about x=0x = 0?
  2. How does the shell method compare to the disk method for this type of problem?
  3. What changes in the formula if the axis of rotation is y=3y = 3 instead of y=0y = 0?
  4. Derive the formula for the shell method in general terms.
  5. How can you visualize the region being rotated in 3D to better understand the setup?

Tip: Always sketch the region and understand the boundaries before applying integral formulas!

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Math Problem Analysis

Mathematical Concepts

Volume of Revolution
Shell Method
Definite Integral
Quadratic Equations

Formulas

Shell Method: V = ∫ 2π(radius)(height) dy
Quadratic Function: x = y^2

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12 or College Level