The radius of a sphere is increasing at a rate of 2 mm/s. How fast is the volume increasing (in mm³/s) when the diameter is 40 mm?

Calculus: Early Transcendentals
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ISBN:9781285741550
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...
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**Mathematics - Calculus Problem**

**Problem Statement:**

The radius of a sphere is increasing at a rate of 2 mm/s. How fast is the volume increasing (in mm³/s) when the diameter is 40 mm?

**Solution Explanation:**

1. **Identifying given values:**
   - The rate of change of the radius, \( dr/dt \), is \( 2 \, \text{mm/s} \).
   - The diameter of the sphere is 40 mm, which means the radius, \( r \), is \( \frac{40}{2} = 20 \, \text{mm} \).

2. **Formula for volume of a sphere:**
   \[
   V = \frac{4}{3} \pi r^3
   \]

3. **Differentiate the volume with respect to time \( t \):**
   \[
   \frac{dV}{dt} = \frac{d}{dt} \left( \frac{4}{3} \pi r^3 \right)
   \]
   Using the chain rule, we get:
   \[
   \frac{dV}{dt} = 4 \pi r^2 \cdot \frac{dr}{dt}
   \]

4. **Substitute the known values into the differentiated formula:**
   - \( r = 20 \, \text{mm} \)
   - \( \frac{dr}{dt} = 2 \, \text{mm/s} \)

   \[
   \frac{dV}{dt} = 4 \pi (20 \, \text{mm})^2 \cdot (2 \, \text{mm/s})
   \]

5. **Calculate the rate of change of the volume:**
   \[
   \frac{dV}{dt} = 4 \pi (400 \, \text{mm}^2) \cdot (2 \, \text{mm/s})
   \]
   \[
   \frac{dV}{dt} = 3200 \pi \, \text{mm}^3/\text{s}
   \]

Hence, the volume of the sphere is increasing at a rate of \( 3200 \pi \, \text{mm}^3/\text{s} \).

**Concepts Covered:**
- Differential calculus
Transcribed Image Text:**Mathematics - Calculus Problem** **Problem Statement:** The radius of a sphere is increasing at a rate of 2 mm/s. How fast is the volume increasing (in mm³/s) when the diameter is 40 mm? **Solution Explanation:** 1. **Identifying given values:** - The rate of change of the radius, \( dr/dt \), is \( 2 \, \text{mm/s} \). - The diameter of the sphere is 40 mm, which means the radius, \( r \), is \( \frac{40}{2} = 20 \, \text{mm} \). 2. **Formula for volume of a sphere:** \[ V = \frac{4}{3} \pi r^3 \] 3. **Differentiate the volume with respect to time \( t \):** \[ \frac{dV}{dt} = \frac{d}{dt} \left( \frac{4}{3} \pi r^3 \right) \] Using the chain rule, we get: \[ \frac{dV}{dt} = 4 \pi r^2 \cdot \frac{dr}{dt} \] 4. **Substitute the known values into the differentiated formula:** - \( r = 20 \, \text{mm} \) - \( \frac{dr}{dt} = 2 \, \text{mm/s} \) \[ \frac{dV}{dt} = 4 \pi (20 \, \text{mm})^2 \cdot (2 \, \text{mm/s}) \] 5. **Calculate the rate of change of the volume:** \[ \frac{dV}{dt} = 4 \pi (400 \, \text{mm}^2) \cdot (2 \, \text{mm/s}) \] \[ \frac{dV}{dt} = 3200 \pi \, \text{mm}^3/\text{s} \] Hence, the volume of the sphere is increasing at a rate of \( 3200 \pi \, \text{mm}^3/\text{s} \). **Concepts Covered:** - Differential calculus
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