3. A circular cone has height 10 and base radius 4. Find the average area of a circular cross-section of the cone.

Calculus: Early Transcendentals
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Author:James Stewart
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Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
Question
**Problem 3:**

A circular cone has a height of 10 units and a base radius of 4 units. Find the average area of a circular cross-section of the cone.

---

To solve this problem, consider the cone's cross-sections parallel to the base. If you take a horizontal slice of the cone at a height \( h \), the radius \( r \) of the slice is proportional to its height from the vertex.

### Explanation:
- The radius \( r \) at any height \( x \) from the vertex is given by the formula:
  \[
  r = \frac{4}{10} \times (10-x) = 2(1-x/5)
  \]
- The area \( A \) of a cross-section is \( \pi r^2 \):
  \[
  A = \pi \left(2\left(1-\frac{x}{5}\right)\right)^2 = 4\pi \left(1-\frac{x}{5}\right)^2
  \]

### Average Area:
To find the average area of these cross-sections from \( x = 0 \) to \( x = 10 \) (top to bottom of the cone), integrate the area function and then divide by the height:

1. Integrate \( A(x) \) from 0 to 10:
  \[
  \int_{0}^{10} 4\pi \left(1-\frac{x}{5}\right)^2 \, dx 
  \]
2. Find the average:
  \[
  \frac{1}{10} \int_{0}^{10} 4\pi \left(1-\frac{x}{5}\right)^2 \, dx 
  \]

By solving the integral and dividing by 10, you get the average cross-sectional area.

---
Transcribed Image Text:**Problem 3:** A circular cone has a height of 10 units and a base radius of 4 units. Find the average area of a circular cross-section of the cone. --- To solve this problem, consider the cone's cross-sections parallel to the base. If you take a horizontal slice of the cone at a height \( h \), the radius \( r \) of the slice is proportional to its height from the vertex. ### Explanation: - The radius \( r \) at any height \( x \) from the vertex is given by the formula: \[ r = \frac{4}{10} \times (10-x) = 2(1-x/5) \] - The area \( A \) of a cross-section is \( \pi r^2 \): \[ A = \pi \left(2\left(1-\frac{x}{5}\right)\right)^2 = 4\pi \left(1-\frac{x}{5}\right)^2 \] ### Average Area: To find the average area of these cross-sections from \( x = 0 \) to \( x = 10 \) (top to bottom of the cone), integrate the area function and then divide by the height: 1. Integrate \( A(x) \) from 0 to 10: \[ \int_{0}^{10} 4\pi \left(1-\frac{x}{5}\right)^2 \, dx \] 2. Find the average: \[ \frac{1}{10} \int_{0}^{10} 4\pi \left(1-\frac{x}{5}\right)^2 \, dx \] By solving the integral and dividing by 10, you get the average cross-sectional area. ---
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