JEE MATHEMATICS MCQ: RATE MEASURE

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A stone is dropped into a quiet lake. If the waves moves in circles at the rate of 30cm/sec when the radius is 50 m, the rate of increase of enclosed area is

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Correct option: A

30\;\pi \;{\mathrm{m}^2}/\mathrm{sec}

Option A (

30 \;\pi \;{\mathrm{m}^2}/\mathrm{sec}

) is correct because the rate of increase of the enclosed area is calculated using the formula

\frac{{dA}}{{dt}} = 2\pi r\frac{{dr}}{{dt}}

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