**Question:**

How many litres of water flow out of a pipe having an area of cross-section of $5 \mathrm{~cm}^{2}$ in one minute, if the speed of water in the pipe is $30 \mathrm{~cm} / \mathrm{sec}$ ?

**Solution:**

Given data is as follows:

Area of cross section of the pipe $=5 \mathrm{~cm}^{2}$

Speed of water = 30 cm/sec

We have to find the volume of water that flows through the pipe in 1 minute.

Volume of water that flows through the pipe in one second $=\pi r^{2} h$

Here, $\pi r^{2}$ is nothing but the cross section of the pipe and $h$ is $30 \mathrm{~cm}$.

Therefore, we have,

Volume of water that flows through the pipe in one second $=5 \times 30=150 \mathrm{~cm}^{3}$

Volume of water that flows through the pipe in one minute $=150 \times 60=9000 \mathrm{~cm}^{3}$

We know that $1000 \mathrm{~cm}^{3}=1$ litre. Therefore,

Volume of water that flows through the pipe in one minute = 9 litres

Hence, the volume of water that flows through the given pipe in 1 minute is 9 litres.