\( -2/π\..." - Step-by-step solution, answer key, and detailed explanation on MCA Prep."> \( -2/π\..." - Step-by-step solution, answer key, and detailed explanation on MCA Prep." /> \( -2/π\..." - Step-by-step solution, answer key, and detailed explanation on MCA Prep." />

Question 15

Logical Reasoning Differentiation Hard

If the radius of the circle changes at the rate of&nbsp;<span class="math-tex">\(\rm-\frac{2}{\pi}\ m/sec\)</span>, at what rate does the circle&#39;s area change when the radius is 10 m?

(A) 40 m<sup>2</sup>/sec
(B) 30&nbsp;m<sup>2</sup>/sec
(C) -30&nbsp;m<sup>2</sup>/sec
(D) -40&nbsp;m<sup>2</sup>/sec
✓ Correct Answer: Option D Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

To find the rate at which the circle's area is changing when the radius is 10 m, we proceed as follows: The area of a circle is given by: \[ A = \pi r^2 \] Differentiating both sides with respect to time \( t \): \[ \frac{dA}{dt} = 2\pi r \frac{dr}{dt} \] We are given: \[ \frac{dr}{dt} = -\frac{2}{\pi} \, \text{m/sec}, \quad r = 10 \, \text{m} \] Substitute the values into the equation: \[ \frac{dA}{dt} = 2\pi (10) \left(-\frac{2}{\pi}\right) \] Simplify: \[ \frac{dA}{dt} = 20\pi \cdot \left(-\frac{2}{\pi}\right) \] \[ \frac{dA}{dt} = -40 \, \text{m}^2/\text{sec} \]

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