Math Problem Statement

The radius of a sphere is increasing at a constant rate of 6 meters per second. At the instant when the radius of the sphere is 5 meters, what is the rate of change of the volume? The volume of a sphere can be found with the equation V, equals, start fraction, 4, divided by, 3, end fraction, pi, r, cubed, .V= 3 4 ​ πr 3 . Round your answer to three decimal places.

Solution

We are given that the radius rr of a sphere is increasing at a constant rate of 6 meters per second, i.e.,

drdt=6m/s.\frac{dr}{dt} = 6 \, \text{m/s}.

We are also given the equation for the volume of the sphere:

V=43πr3.V = \frac{4}{3} \pi r^3.

We are asked to find the rate of change of the volume dVdt\frac{dV}{dt} when the radius is r=5r = 5 meters.

Step 1: Differentiate the volume formula with respect to time tt.

Using the chain rule, we differentiate V=43πr3V = \frac{4}{3} \pi r^3 with respect to tt:

dVdt=ddt(43πr3).\frac{dV}{dt} = \frac{d}{dt} \left( \frac{4}{3} \pi r^3 \right).

Applying the chain rule:

dVdt=43π3r2drdt.\frac{dV}{dt} = \frac{4}{3} \pi \cdot 3r^2 \cdot \frac{dr}{dt}.

Simplifying:

dVdt=4πr2drdt.\frac{dV}{dt} = 4 \pi r^2 \cdot \frac{dr}{dt}.

Step 2: Substitute the known values.

We know drdt=6m/s\frac{dr}{dt} = 6 \, \text{m/s} and r=5mr = 5 \, \text{m}. Substitute these values into the equation:

dVdt=4π(5)26.\frac{dV}{dt} = 4 \pi (5)^2 \cdot 6.

dVdt=4π256.\frac{dV}{dt} = 4 \pi \cdot 25 \cdot 6.

dVdt=600π.\frac{dV}{dt} = 600 \pi.

Step 3: Approximate the value.

Using π3.1416\pi \approx 3.1416:

dVdt6003.1416=1884.96m3/s.\frac{dV}{dt} \approx 600 \cdot 3.1416 = 1884.96 \, \text{m}^3/\text{s}.

Thus, the rate of change of the volume when the radius is 5 meters is approximately:

1884.961m3/s.\boxed{1884.961} \, \text{m}^3/\text{s}.

Additional Questions:

  1. How does the rate of change of the volume change if the radius increases at a different rate?
  2. What would be the rate of change of the volume when the radius is 10 meters?
  3. How would the rate of change of the volume behave if the radius were decreasing instead of increasing?
  4. How can you use implicit differentiation to solve similar problems involving other geometric shapes?
  5. How would this formula change if the sphere had a different geometric constant?

Tip: Always carefully apply the chain rule when dealing with rates of change of related quantities in calculus.

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Math Problem Analysis

Mathematical Concepts

Calculus
Related Rates
Geometry

Formulas

V = (4/3)πr^3
dV/dt = 4πr^2 * dr/dt

Theorems

Chain Rule

Suitable Grade Level

Grades 11-12