Question:medium

The rate of change (in cm2/s) of the total surface area of a hemisphere with respect to the radius r at r = 3.

Show Hint

When differentiating functions that involve powers of variables, such as \( r^2 \), apply the power rule: \( \frac{d}{dr}(r^n) = n r^{n-1} \). This simplifies the process significantly. Also, remember to substitute numerical values carefully and check cube roots or other roots to ensure the calculation is correct before substituting them into your derivative expression.

Updated On: Mar 27, 2026
  • 66π
  • 6.6π
  • 3.3π
  • 4.4π
Show Solution

The Correct Option is B

Solution and Explanation

The formula for the total surface area \( S \) of a hemisphere is \( S = 3\pi r^2 \). Differentiating \( S \) with respect to \( r \) yields \( \frac{dS}{dr} = 6\pi r \). Given \( r = \sqrt[3]{1.331} \), we first calculate \( r \). Since \( 1.1^3 = 1.331 \), \( r = 1.1 \). Substituting this value into the derivative, we get \( \frac{dS}{dr} = 6\pi (1.1) = 6.6\pi \). Therefore, the rate of change of the total surface area with respect to the radius is \( 6.6\pi \).

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