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MHT CET202121 Sep 2021Morning ShiftMathematicsApplication of DerivativesActual

A stone is dropped in a quiet lake and it is observed that waves move in circles, If the radius of a circular wave increases at the rate 2 ~cm / sec , then the rate of increase in its area at the instant when its radius is 10 ~cm , is cm ^2 / sec .

Options

  1. A40
  2. B80
  3. C10
  4. D20

Correct answer

A. 40

Step-by-step solution

Given d r d t =2 ~cm / sec r=10 ~cm We have A= r^2 Diff. w.r.t. t aligned & d A d t =2 r d r d t & =2 10 2 & =40 aligned

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