Question:

A spherical balloon is expanding. If the radius is increasing at the rate of $2$ centimeters per minute, the rate at which the volume increases (in cubic centimeters per minute) when the radius is $5$ centimetres is

Updated On: Apr 28, 2024
  • 10$\pi$
  • 100$\pi$
  • 200$\pi$
  • 50$\pi$
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The Correct Option is C

Solution and Explanation

Let r and V be the respectively radius and volume of the balloon. Let t represents the time. The rate of increament in radius is $\frac{dr}{dt}=2$ cm/minute. The volume of the balloon is given by
$V =\frac{4}{3}\pi r^{3}$
Differentiating w.r. to t, we get
$\frac{dV}{dt}=\frac{4}{3}\pi\left(3r^{2}\frac{dr}{dt}\right)$
Substituting the values of and $\frac{dr}{dt}$ , we get
$\frac{dV}{dt}=\frac{4}{3}\pi\left(3\times5^{2}\times2\right)=200\pi cm^{3} / minute$
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Concepts Used:

Application of Derivatives

Various Applications of Derivatives-

Rate of Change of Quantities:

If some other quantity ‘y’ causes some change in a quantity of surely ‘x’, in view of the fact that an equation of the form y = f(x) gets consistently pleased, i.e, ‘y’ is a function of ‘x’ then the rate of change of ‘y’ related to ‘x’ is to be given by 

\(\frac{\triangle y}{\triangle x}=\frac{y_2-y_1}{x_2-x_1}\)

This is also known to be as the Average Rate of Change.

Increasing and Decreasing Function:

Consider y = f(x) be a differentiable function (whose derivative exists at all points in the domain) in an interval x = (a,b).

  • If for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≤ f(x2); then the function f(x) is known as increasing in this interval.
  • Likewise, if for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≥ f(x2); then the function f(x) is known as decreasing in this interval.
  • The functions are commonly known as strictly increasing or decreasing functions, given the inequalities are strict: f(x1) < f(x2) for strictly increasing and f(x1) > f(x2) for strictly decreasing.

Read More: Application of Derivatives