Chapter 5: Problem 11
Find the centroid of the region bounded by the given curves. Make a sketch and use symmetry where possible. $$ y=x^{3}, y=0, x=1 $$
Short Answer
Expert verified
Centroid is at \( \left( \frac{4}{5}, \frac{2}{7} \right) \).
Step by step solution
01
Understand the Problem
We need to find the centroid of a region bounded by the curves \( y = x^3 \), \( y = 0 \), and \( x = 1 \). This region lies above the x-axis, below the curve, and extends from \( x = 0 \) to \( x = 1 \).
02
Identify the Boundaries
The boundaries of the region are given by \( y = x^3 \) (upper boundary), \( y = 0 \) (lower boundary), and vertical lines \( x = 0 \) and \( x = 1 \). We work in the first quadrant, ensuring the area lies between these bounds.
03
Calculate the Area of the Region
The area \( A \) of the region is \[ A = \int_{0}^{1} (x^3 - 0) \, dx = \int_{0}^{1} x^3 \, dx = \left[ \frac{x^4}{4} \right]_{0}^{1} = \frac{1}{4}. \]
04
Find the x-coordinate of the Centroid
The x-coordinate \( \bar{x} \) of the centroid is given by \[ \bar{x} = \frac{1}{A} \int_{0}^{1} x (x^3) \, dx = 4 \int_{0}^{1} x^4 \, dx = 4 \left[ \frac{x^5}{5} \right]_{0}^{1} = 4 \cdot \frac{1}{5} = \frac{4}{5}. \]
05
Find the y-coordinate of the Centroid
The y-coordinate \( \bar{y} \) of the centroid is calculated by\[ \bar{y} = \frac{1}{A} \int_{0}^{1} \frac{x^3 + 0}{2} x^3 \, dx = 4 \cdot \frac{1}{2} \int_{0}^{1} x^6 \, dx = 2 \left[ \frac{x^7}{7} \right]_{0}^{1} = 2 \cdot \frac{1}{7} = \frac{2}{7}. \]
06
Conclusion - Centroid Coordinates
The coordinates of the centroid are found to be \( \left( \frac{4}{5}, \frac{2}{7} \right) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Region Bounded by Curves
To find the centroid of a region, we must first identify the region's shape. The region in question is defined by the curves and lines: \( y = x^3 \), \( y = 0 \), and \( x = 1 \). Imagining this on the Cartesian plane:
- \( y = x^3 \) is a curve starting from the origin and curving upward as \( x \) increases.
- \( y = 0 \) represents the x-axis, which acts as a lower boundary.
- Finally, \( x = 1 \) is a vertical line, marking the end of our region horizontally.
Integration
Integration helps us find areas and averages in calculus, which are crucial in determining centroids. The area \( A \) of our region is found by integrating the function \( y = x^3 \) from \( x=0 \) to \( x=1 \). This is done as follows:\[ A = \int_{0}^{1} x^3 \, dx \]The process of integration gives us the accumulated value of \( x^3 \) over the interval, found to be \( \frac{1}{4} \). Finding this area is the first step toward identifying the centroid because it will be used to calculate the average positions of \( x \) and \( y \). Integration is also employed to compute the weighted sums of positions—these later steps are crucial for determining the x-coordinate and y-coordinate of the centroid. Thus, integration is more than just finding areas; it's about utilizing these calculations for positional averages.
x-coordinate and y-coordinate calculations
The centroid (\( \bar{x}, \bar{y} \)) represents the geometric center of the region. We compute this using weighted averages of the x and y positions. To find the x-coordinate \( \bar{x} \): - We use the weighted integral of \( x \) times the function: \[ \bar{x} = \frac{1}{A} \int_{0}^{1} x \cdot x^3 \, dx = \frac{4}{5} \]This indicates that the balance point along the x-axis happens around \( 0.8 \).For the y-coordinate \( \bar{y} \):- The formula considers the average value of the function, \[ \bar{y} = \frac{1}{A} \int_{0}^{1} \frac{x^3}{2} x^3 \, dx = \frac{2}{7} \]This signifies the average y-position or height of the region is approximately \(0.286\).These calculations secure the coordinates of the centroid as \( \left( \frac{4}{5}, \frac{2}{7} \right) \), which centers our region both horizontally and vertically, fulfilling the requirement of finding where the region naturally balances.