Question:

If there is an error of $k\%$ in measuring the edge of a cube, then the percent error in estimating its volume is

Updated On: Apr 15, 2024
  • $k$
  • $3k$
  • $\frac{k}{3}$
  • None of these
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The Correct Option is B

Solution and Explanation

We know that, the volume V of a cube of side x is given by
$V = x^3$
On differenting w. r. t, we get
$\Rightarrow \frac{dv}{dx} = 3 x^2$
Let the change in $x$ be $\Delta x = K \%$ of $x = \frac{kx}{100}$
Now, the change in volume.
$\Delta V = \left( \frac{dV}{dx}\right) \Delta x = 3x^2 ( \Delta x)$
$= 3x^{2} \left(\frac{kx}{100}\right) = \frac{3x^{2} . k}{100} $
$\therefore$ Approximate change in volume
$=\frac{3kx^{3}}{100} = \frac{3k}{100} . x^{3} $
$= 3k \%$ of original volume
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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