Water is being poured at the rate of $36 \mathrm{~m}^3 / \mathrm{min}$ into a cylindrical vessel, whose…

Water is being poured at the rate of $36 \mathrm{~m}^3 / \mathrm{min}$ into a cylindrical vessel, whose circular base is of radius 3 meters. Then the water level in the cylinder is rising at the rate of
  1. $4 \pi \mathrm{~m} / \mathrm{min}$
  2. $\frac{4}{\pi} \mathrm{~m} / \mathrm{min}$
  3. $\frac{1}{4 \pi} \mathrm{~m} / \mathrm{min}$
  4. $\frac{\pi}{4} \mathrm{~m} / \mathrm{min}$

Solution

$\begin{aligned} & \frac{\mathrm{dV}}{\mathrm{dt}}=36 \mathrm{~m}^3 / \mathrm{min}, \text { radius }(\mathrm{r})=3 \mathrm{~m} \\ & \text { Volume }(\mathrm{V})=\pi \mathrm{r}^2 \mathrm{~h} \\ \therefore \quad & \frac{\mathrm{dV}}{\mathrm{dt}}=\pi \mathrm{r}^2 \frac{\mathrm{dh}}{\mathrm{dt}} \\ \Rightarrow & 36=\pi \times(3)^2 \frac{\mathrm{dh}}{\mathrm{dt}} \\ \Rightarrow & \frac{\mathrm{dh}}{\mathrm{dt}}=\frac{4}{\pi} \mathrm{~m} / \mathrm{min}\end{aligned}$

Asked in: MHT CET 2024 (16 May Shift 2)

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