Math Problem Statement

Find the centroid of the region bounded by the given curves. x = 10 − y2, x = 0

Solution

The problem asks for the centroid of the region bounded by the curves x=10y2x = 10 - y^2 and x=0x = 0.

Step 1: Identify the region

The first equation, x=10y2x = 10 - y^2, is a parabola that opens to the left, with its vertex at (10,0)(10, 0). The second equation, x=0x = 0, is the yy-axis, meaning we are looking for the region between these two curves.

Step 2: Find the bounds of integration

To find the bounds, we need to determine where the curves intersect, which occurs when x=0x = 0: 0=10y20 = 10 - y^2 y2=10y^2 = 10 y=±10y = \pm \sqrt{10}

Thus, the region is bounded vertically between y=10y = -\sqrt{10} and y=10y = \sqrt{10}.

Step 3: Compute the area of the region

The formula for the area of the region is: A=y1y2(xrightxleft)dyA = \int_{y_1}^{y_2} (x_{\text{right}} - x_{\text{left}}) \, dy Here, xright=10y2x_{\text{right}} = 10 - y^2 and xleft=0x_{\text{left}} = 0, so: A=1010(10y2)dyA = \int_{-\sqrt{10}}^{\sqrt{10}} (10 - y^2) \, dy

Now, calculate the integral: A=101010dy1010y2dyA = \int_{-\sqrt{10}}^{\sqrt{10}} 10 \, dy - \int_{-\sqrt{10}}^{\sqrt{10}} y^2 \, dy The first integral is: 101010dy=10(210)=2010\int_{-\sqrt{10}}^{\sqrt{10}} 10 \, dy = 10 \cdot (2\sqrt{10}) = 20\sqrt{10} The second integral is: 1010y2dy=23(103/2)=20103\int_{-\sqrt{10}}^{\sqrt{10}} y^2 \, dy = \frac{2}{3} \cdot (10^{3/2}) = \frac{20\sqrt{10}}{3}

Thus, the total area is: A=201020103=6010320103=40103A = 20\sqrt{10} - \frac{20\sqrt{10}}{3} = \frac{60\sqrt{10}}{3} - \frac{20\sqrt{10}}{3} = \frac{40\sqrt{10}}{3}

Step 4: Compute the centroid coordinates

The centroid (xˉ,yˉ)(\bar{x}, \bar{y}) is given by the following formulas:

xˉ=1Ay1y2xright(xrightxleft)dy\bar{x} = \frac{1}{A} \int_{y_1}^{y_2} x_{\text{right}} \cdot (x_{\text{right}} - x_{\text{left}}) \, dy yˉ=12Ay1y2y(xrightxleft)dy\bar{y} = \frac{1}{2A} \int_{y_1}^{y_2} y \cdot (x_{\text{right}} - x_{\text{left}}) \, dy

Compute xˉ\bar{x}:

xˉ=1A1010(10y2)(10y2)dy\bar{x} = \frac{1}{A} \int_{-\sqrt{10}}^{\sqrt{10}} (10 - y^2)(10 - y^2) \, dy Expanding: (10y2)2=10020y2+y4(10 - y^2)^2 = 100 - 20y^2 + y^4 So: xˉ=1401031010(10020y2+y4)dy\bar{x} = \frac{1}{\frac{40\sqrt{10}}{3}} \int_{-\sqrt{10}}^{\sqrt{10}} (100 - 20y^2 + y^4) \, dy Each term integrates as follows: 1010100dy=100210=20010\int_{-\sqrt{10}}^{\sqrt{10}} 100 \, dy = 100 \cdot 2\sqrt{10} = 200\sqrt{10} 101020y2dy=2020103=400103\int_{-\sqrt{10}}^{\sqrt{10}} 20y^2 \, dy = 20 \cdot \frac{20\sqrt{10}}{3} = \frac{400\sqrt{10}}{3} 1010y4dy=25(105/2)=200105=4010\int_{-\sqrt{10}}^{\sqrt{10}} y^4 \, dy = \frac{2}{5} \cdot (10^{5/2}) = \frac{200\sqrt{10}}{5} = 40\sqrt{10}

Thus, xˉ\bar{x} becomes: xˉ=34010(20010400103+4010)\bar{x} = \frac{3}{40\sqrt{10}} \left( 200\sqrt{10} - \frac{400\sqrt{10}}{3} + 40\sqrt{10} \right) Simplifying: xˉ=3401020010+120103=12040=3\bar{x} = \frac{3}{40\sqrt{10}} \cdot \frac{200\sqrt{10} + 120\sqrt{10}}{3} = \frac{120}{40} = 3

Compute yˉ\bar{y}:

yˉ=12A1010y(10y2)dy\bar{y} = \frac{1}{2A} \int_{-\sqrt{10}}^{\sqrt{10}} y (10 - y^2) \, dy This is an odd function, so: yˉ=0\bar{y} = 0

Final answer:

The centroid of the region is (3,0)(3, 0).

Do you want further details or have any questions?

Here are some related problems to explore:

  1. Find the centroid of a region bounded by y=x2y = x^2 and y=0y = 0.
  2. Find the area of the region bounded by y=xy = \sqrt{x} and y=x2y = x - 2.
  3. Compute the volume of a solid of revolution formed by rotating x=10y2x = 10 - y^2 around the yy-axis.
  4. Determine the centroid of the region bounded by y=sinxy = \sin x and the xx-axis from x=0x = 0 to x=πx = \pi.
  5. Find the centroid of the region bounded by x2+y2=9x^2 + y^2 = 9 and x=0x = 0.

Tip: When finding centroids, check for symmetry—it can often simplify calculations.

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Math Problem Analysis

Mathematical Concepts

Calculus
Centroids
Area under curves
Definite Integration

Formulas

Centroid coordinates: (\bar{x}, \bar{y}) = \left( \frac{1}{A} \int x \, dA, \frac{1}{A} \int y \, dA \right)
Area of region: A = \int_{y_1}^{y_2} (x_{right} - x_{left}) \, dy

Theorems

Symmetry theorem (used to determine \bar{y} = 0)
Integration techniques for centroids

Suitable Grade Level

College Calculus or Advanced High School (Grades 11-12)