Question

A cylindrical pipe has inner diameter of 7 cm and water flows through it at the rate of 192.5 litres per minute. Find the rate of flow in kilometres per hour.

• A. 1
• B. 3
• C. 5
• D. 6

Answer 1

The correct option is B

3

In one minute 192.5 litres of water flows.

So, The Volume of water that flows in one hour = (192.50 $\times$ 60) liters. [$\because 1\text{hour}=60\text{mins}$ ]

Volume in ${\text{cm}}^3$ = (192.5 $\times$ 60 $\times$ 1000) ${\text{cm}}^3$ [$\because 1\text{litre}=1000{\text{cm}}^3$ ]

Inner radius of the pipe = 3.5 cm.

Let the length of column of water that flows in 1 hour be h cm.

Then,$\frac{22}{7}$ $\times$ 3.5 $\times$ 3.5 $\times$ h = 192.5 $\times$ 60 $\times$ 1000

h= 300000 cm = 3 km

Hence, the rate of flow = 3 km per hour.