Question : Water is being pumped out through a circular pipe whose internal diameter is 7 cm. If the flow of water is 12 cm per second, how many litres of water are being pumped out in one hour?
Option 1: 1663.2 litres
Option 2: 1500 litres
Option 3: 1747.6 litres
Option 4: 2000 litres
Correct Answer: 1663.2 litres
Solution :
Given: Diameter = 7 cm
Radius = $\frac{7}{2}$ cm
Rate of flow = 12 cm per sec
The volume of the pipe = $\pi r^2 h$, where $r$ and $h$ are the radius and height of the pipe.
= $\frac{22}{7}×\frac{7}{2}×\frac{7}{2}×12$
= 462 cm$^3$
Volume of water flowing in one hour = 462 × 3600 cm$^3$ = 1663200 cm$^3$
= $\frac{1663200}{1000}$ litres
= 1663.2 litres
Hence, the correct answer is 1663.2 litres.
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