We have,
Diameter of cylindrical tank = 1.4 m
Radius of tank = d/2 = 1.4/2 = 0.7 m
Height of tank = 2.1 m
Diameter of pipe flowing water in tank = 3.5 cm
Radius of pipe = d/2 = 3.5/2 cm
Rate of flow of water = 2 m/s
Time taken to fill the tank = volume of tank / volume of pipe × rate of flow
= πr‑2h / (πr‑2 × 2)
= (π × 0.7 × 0.7 × 2.1) / (π × 3.5/2 × 3.5/2 × 2)
= 1.029 / 6.125
= 0.168
= 1680 seconds
= 128 minutes.
∴ Time taken to fill the tank is 128 minutes.