Math Problem Statement

Find the coordinates of the centroid of the region bounded by

y equals x squaredy=x2

and

y equals 4.y=4.

The region is covered by a​ thin, flat plate.

Solution

To find the coordinates of the centroid of the region bounded by the curves y=x2y = x^2 and y=4y = 4, we follow a similar process as before.

1. Find the Points of Intersection:

First, we determine where the curves intersect by setting y=x2y = x^2 equal to y=4y = 4:

x2=4x^2 = 4

x=±2x = \pm 2

So, the curves intersect at the points (2,4)(-2, 4) and (2,4)(2, 4).

2. Set Up the Integral for the Centroid:

The centroid (xˉ,yˉ)(\bar{x}, \bar{y}) of the region can be found using the formulas:

xˉ=1Aabx[f(x)g(x)]dx\bar{x} = \frac{1}{A} \int_{a}^{b} x \left[ f(x) - g(x) \right] dx

yˉ=1Aab12[f(x)2g(x)2]dx\bar{y} = \frac{1}{A} \int_{a}^{b} \frac{1}{2} \left[ f(x)^2 - g(x)^2 \right] dx

where:

  • f(x)=4f(x) = 4 (the upper curve),
  • g(x)=x2g(x) = x^2 (the lower curve),
  • a=2a = -2, b=2b = 2 (the limits of integration),
  • AA is the area of the region.

3. Calculate the Area AA:

The area AA of the region is given by:

A=22(4x2)dxA = \int_{-2}^{2} \left(4 - x^2\right) dx

Calculating this integral:

A=[4xx33]22A = \left[ 4x - \frac{x^3}{3} \right]_{-2}^{2}

[ A = \left[ (4 \times 2) - \frac{2^3}{3} \right] - \left[ (4 \times -2) - \frac{(-2)^3}{3} \right] ]

A=(883)(8+83)A = \left(8 - \frac{8}{3}\right) - \left(-8 + \frac{-8}{3}\right)

A=(24383)+(24383)=323A = \left(\frac{24}{3} - \frac{8}{3}\right) + \left(\frac{24}{3} - \frac{-8}{3}\right) = \frac{32}{3}

4. Calculate xˉ\bar{x}:

Now, we calculate xˉ\bar{x}:

xˉ=1A22x(4x2)dx\bar{x} = \frac{1}{A} \int_{-2}^{2} x \left(4 - x^2\right) dx

Since 22x(4x2)dx\int_{-2}^{2} x \cdot (4 - x^2) dx is an odd function over a symmetric interval, the integral evaluates to 0:

xˉ=0\bar{x} = 0

5. Calculate yˉ\bar{y}:

Now, we calculate yˉ\bar{y}:

yˉ=1A2212[42(x2)2]dx\bar{y} = \frac{1}{A} \int_{-2}^{2} \frac{1}{2} \left[4^2 - (x^2)^2\right] dx

yˉ=3321222(16x4)dx\bar{y} = \frac{3}{32} \cdot \frac{1}{2} \int_{-2}^{2} \left(16 - x^4\right) dx

Breaking this into two integrals:

yˉ=332[16xx55]22\bar{y} = \frac{3}{32} \left[16x - \frac{x^5}{5}\right]_{-2}^{2}

yˉ=332(32325)=332×1285=125\bar{y} = \frac{3}{32} \left(32 - \frac{32}{5}\right) = \frac{3}{32} \times \frac{128}{5} = \frac{12}{5}

Final Answer:

The centroid (xˉ,yˉ)(\bar{x}, \bar{y}) of the region is:

(0,125)\left(0, \frac{12}{5}\right)

Would you like any further details or have any questions? Here are five related questions you might find interesting:

  1. How does the centroid change if the upper boundary is a different function?
  2. What are some real-life applications of finding centroids in physics or engineering?
  3. Can the method of finding centroids be extended to regions in three dimensions?
  4. How does the symmetry of a region affect the location of its centroid?
  5. How would you find the centroid if the region is bounded by a curve and a line?

Tip: When dealing with centroids, always check for symmetry in the region. Symmetry can simplify the computation of the centroid's coordinates.

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Math Problem Analysis

Mathematical Concepts

Calculus
Integration
Centroid

Formulas

Centroid formulas for area under a curve

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

College