Math Problem Statement

The circumference of a sphere was measured to be 86 cm with a possible error of 0.5 cm. (a) Use differentials to estimate the maximum error (in cm²) in the calculated surface area. (b) Use differentials to estimate the maximum error (in cm³) in the calculated volume. What are the relative errors?

Solution

Let's solve the problem by breaking it down step by step.

Given:

  • The circumference of the sphere C=86C = 86 cm
  • The possible error in measurement of the circumference dC=0.5dC = 0.5 cm

(a) Estimating the maximum error in surface area:

  1. Formula for the circumference of a sphere: C=2πrC = 2\pi r Solving for the radius rr: r=C2πr = \frac{C}{2\pi}

  2. Surface area of a sphere: A=4πr2A = 4\pi r^2

  3. Differential of the surface area: The differential dAdA, representing the maximum error in surface area, is: dA=dAdrdr=8πrdrdA = \frac{dA}{dr} \cdot dr = 8\pi r \, dr Here, drdr is the error in the radius. To find drdr, we differentiate the expression for circumference: C=2πrdC=2πdrdr=dC2πC = 2\pi r \quad \Rightarrow \quad dC = 2\pi \, dr \quad \Rightarrow \quad dr = \frac{dC}{2\pi} Now, substitute this into dAdA.

  4. Relative error: The relative error for surface area is given by: Relative Error=dAA\text{Relative Error} = \frac{dA}{A}

(b) Estimating the maximum error in volume:

  1. Volume of a sphere: V=43πr3V = \frac{4}{3} \pi r^3

  2. Differential of the volume: The differential dVdV, representing the maximum error in volume, is: dV=dVdrdr=4πr2drdV = \frac{dV}{dr} \cdot dr = 4\pi r^2 \, dr

  3. Relative error: The relative error for volume is given by: Relative Error=dVV\text{Relative Error} = \frac{dV}{V}


Let me calculate each part step-by-step for you based on these formulas.Here are the results for the given problem:

(a) Surface Area:

  • The maximum error in surface area is 27cm227 \, \text{cm}^2 (rounded to the nearest integer).
  • The relative error in surface area is 0.0120.012 (rounded to three decimal places).

(b) Volume:

  • The maximum error in volume is 187cm3187 \, \text{cm}^3 (rounded to the nearest integer).
  • The relative error in volume is 0.0170.017 (rounded to three decimal places).

Would you like more details on any step or have any questions?

Here are some related questions:

  1. How does the radius influence the error in surface area?
  2. How would increasing the possible error in circumference affect the maximum error in surface area?
  3. What happens to the relative error if the sphere's circumference is smaller?
  4. Can you use this method to estimate errors in other geometric shapes?
  5. How does the use of differentials help in error estimation?

Tip: Using differentials for error estimation is highly effective for small measurement errors, as it approximates changes in functions for tiny variations.

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Math Problem Analysis

Mathematical Concepts

Differentials
Geometry
Error Estimation
Relative Error

Formulas

Circumference of a sphere: C = 2πr
Surface Area of a sphere: A = 4πr²
Volume of a sphere: V = (4/3)πr³
Differential of Surface Area: dA = 8πr * dr
Differential of Volume: dV = 4πr² * dr
Relative Error: Relative Error = dA/A or dV/V

Theorems

Differential Approximation
Error Propagation

Suitable Grade Level

Grades 11-12, College