Question

The radius of a cylindrical cistern is 10 metres and its height is 15 metres. Initially the cistern is empty, we start filling the cistern with water through a pipe whose diameter is 50 cm, water is coming out of the pipe with a velocity of 5 m/s. How many minutes will it take in filling the cistern with water?

• A. 20
• B. 40
• C. 60
• D. 80

Answer 1

Answer: (D)

80

Answer 2

Here Flow rate = Volume = $\frac{Are}{Height}$
The Volume of cylinder = Area of pipe × velocity × time
time = $\frac{\pi r^2 h}{\pi R^2} ×v$
t =$\frac{\pi \times 10^2 \times 15}{\pi \times (0.25)^2 \times 5}$
t = 4800 seconds
t = $\frac{4800}{60}$ minutes
t = 80 minutes
The correct option is (D)