1.

At what rate will the lateral surface area of the cylinder increase if the radius is increasing at the rate of 2 cm/s when the radius is 5 cm and height is 10 cm?(a) 40 cm/s(b) 40π cm/s(c) 400π cm/s(d) 20π cm/sI had been asked this question in a national level competition.This is a very interesting question from Derivatives Application in section Application of Derivatives of Mathematics – Class 12

Answer»

Correct answer is (b) 40π cm/s

Explanation: Let R be the radius and h be the HEIGHT of the CYLINDER. Then,

\(\frac{dr}{DT}\)=2 cm/s

The AREA of the cylinder is given by A=2πrh

\(\frac{dA}{dt}\)=2πh(\(\frac{dr}{dt}\))=4πh=4π(10)=40π cm/s.



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