Math Problem Statement

The volume of a sphere is decreasing at a constant rate of 6031 cubic centimeters per second. At the instant when the volume of the sphere is 32923292 cubic centimeters, what is the rate of change of the radius? 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

To find the rate of change of the radius drdt\frac{dr}{dt}, given the rate of change of the volume dVdt\frac{dV}{dt}, we can use the formula for the volume of a sphere:

V=43πr3V = \frac{4}{3} \pi r^3

Step 1: Differentiate the volume equation

Differentiate both sides of the volume equation with respect to time tt to relate the rate of change of the volume to the rate of change of the radius.

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

Step 2: Rearrange to solve for drdt\frac{dr}{dt}

We can rearrange this equation to solve for drdt\frac{dr}{dt}:

drdt=dVdt4πr2\frac{dr}{dt} = \frac{\frac{dV}{dt}}{4 \pi r^2}

Step 3: Find the radius rr

We know the volume at the given moment is V=32,923,292V = 32,923,292 cubic centimeters. Use the formula for the volume of a sphere to solve for rr.

V=43πr3V = \frac{4}{3} \pi r^3

Substitute V=32,923,292V = 32,923,292:

32,923,292=43πr332,923,292 = \frac{4}{3} \pi r^3

Now solve for rr:

r3=32,923,292×34πr^3 = \frac{32,923,292 \times 3}{4 \pi}

r398,769,87612.56637r^3 \approx \frac{98,769,876}{12.56637}

r37,861,974r^3 \approx 7,861,974

r7,861,9743r \approx \sqrt[3]{7,861,974}

r198.41cmr \approx 198.41 \, \text{cm}

Step 4: Use the radius to find drdt\frac{dr}{dt}

Now substitute r198.41cmr \approx 198.41 \, \text{cm}, dVdt=6031cm3/s\frac{dV}{dt} = -6031 \, \text{cm}^3/\text{s}, and π3.1416\pi \approx 3.1416 into the equation for drdt\frac{dr}{dt}:

drdt=60314π(198.41)2\frac{dr}{dt} = \frac{-6031}{4 \pi (198.41)^2}

drdt60314×3.1416×39368.97\frac{dr}{dt} \approx \frac{-6031}{4 \times 3.1416 \times 39368.97}

drdt6031494,689.15\frac{dr}{dt} \approx \frac{-6031}{494,689.15}

drdt0.0122cm/s\frac{dr}{dt} \approx -0.0122 \, \text{cm/s}

Final Answer:

The rate of change of the radius is approximately 0.012cm/s-0.012 \, \text{cm/s} (rounded to three decimal places).

Do you want more details, or do you have any questions?

Here are five related questions for further exploration:

  1. How would the rate of change of the radius vary if the volume decreased at a faster rate?
  2. What would happen to drdt\frac{dr}{dt} if the radius were twice as large at this instant?
  3. How does the surface area of the sphere change with time?
  4. If the rate of volume decrease were halved, how would that affect drdt\frac{dr}{dt}?
  5. What would the rate of change of the radius be at the moment when the volume is half of 32,923,292 cm³?

Tip: When solving related rates problems, always differentiate the known formula with respect to time to establish a connection between the variables.

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Math Problem Analysis

Mathematical Concepts

Calculus
Related Rates
Geometry

Formulas

Volume of a sphere: V = (4/3)πr^3
Rate of change of volume: dV/dt = 4πr^2(dr/dt)

Theorems

Related Rates Theorem

Suitable Grade Level

Grades 11-12