Question

# Water is being pumped out through a circular pipe whose internal diameter is 7 cm. If the flow of water is 72 cm per second, how many liters of water are being pumped out in one hour?

Hint: Here we go through by finding the volume of water that is flown in one second by taking the height of a cylinder as 72 cm because in one second it flows 72 cm of water. And then we find out the volume of water that flows in one hour.

According to the question it is given that, Diameter of the pipe =7 cm.
Thus, Radius of pipe, r$= \dfrac{7}{2}cm$.
And for calculating the volume of water that is flown in one second we have to take the height of the pipe as 72 cm because in one second it flows 72 cm of water.
And we know that the volume of the cylinder is $\pi {r^2}h$ and the pipe is also in the shape of the cylinder so apply this formula to find the volume of water that flowed in one second.
Volume of water flowed$= \pi {r^2}h$.
$\Rightarrow \dfrac{{22}}{7} \times \dfrac{7}{2} \times \dfrac{7}{2} \times 72 = 2772c{m^3}$ I.e. 2.772 liter because $1000 c{m^3} = 1 litre$
And now for finding the water pumped out in an hour we have to calculate the number of seconds in one hour. As we know, 1 hour= 60 minute and 1 minute= 60 second. So by applying this condition we can say that 1 hour$= 60 \times 60 = 3600$seconds.
I.e. $2.772 \times 3600 = 9979.2$ liter.