Question

water is supplied to a city population for general use from a river through a cylindrical pipe. the radius of the cross section of pipe is 10cm. the speed of water through the pipe is 18km per hour. find the quantity of water in litres which is supplied to the city in 2 hours.

Answer 1

Radius of the cross section of the pipe = 10 cm
so, area of cross section of pipe = ${\mathrm{\pi r}}^2=\frac{22}{7}\times {\left(10\right)}^2=\frac{2200}{7}{\mathrm{cm}}^2$
Speed of the water through the pipe = 18 km/hr
Then length of column of water flown in 2 hours = $18\times 2$ = 36 km = $36\times 1000\times 100$ = 3600000 cm
So volume of water flown = $\mathrm{area}\mathrm{of}\mathrm{cross}\mathrm{section}\mathrm{of}\mathrm{pipe}\times \mathrm{length}\mathrm{of}\mathrm{column}\mathrm{of}\mathrm{water}\mathrm{flown}$
= $\frac{2200}{7}\times 3600000=792\times {10}^7{\mathrm{cm}}^3=\frac{792\times {10}^7}{{10}^3}=792\times {10}^4\mathrm{litres}$
Therefore the quantity of water that flows in 2 hours is $792\times {10}^4$ litres.