This page offers a step-by-step solution to the specific question **NCERT Class 12th Mathematics - Application of Derivatives | the radius of an air bubble is increasing at the r Answer ** from NCERT Class 12th Mathematics, Chapter Application of Derivatives.

Question 12

The radius of an air bubble is increasing at the rate of 1/2 cm/s. At what rate is the volume of the bubble increasing when the radius is 1 cm?

Answer

The air bubble is in the shape of a sphere.

Now, the volume of an air bubble (*V*) with radius (*r*) is given by,

\begin{align} V = \frac{4}{3}\pi r^3 \end{align}

The rate of change of volume (*V)* with respect to time (*t)* is given by,

\begin{align} \frac{dV}{dt} = \frac{4}{3}\pi \frac{d}{dr}(r^3).\frac{dr}{dt} \;\;\;[By\; Chain\; Rule] \end{align}

\begin{align} = \frac{4}{3}\pi (3r^2).\frac{dr}{dt} \end{align}

\begin{align} = \frac{4}{3}\pi r^2.\frac{dr}{dt} \end{align}

It is given that

\begin{align} \frac{dr}{dt}=\frac{1}{2} cm/s .\end{align}

Therefore, when *r* = 1 cm,

\begin{align} \frac{dV}{dt}=4\pi(1)^2.(\frac{1}{2})=2\pi\; cm^3/s \end{align}

Hence, the rate at which the volume of the bubble increases is 2π cm^{3}/s.

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Dhriti
2016-04-15 10:12:36

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