Water flows into a tank 180 m × 140 m through a rectangular pipe of 1.2m × 0.75 m at a rate of 15 km/h. In what time will the water rise by 4 m?

7 hours 28 minutes

Let 'x' hours the water level in the tank rise by 4 m.

Discharge of water = Volume of tank upto water level in the tank.

Discharge of water = Area of cross-section of pipe × velocity of flow,

From above formulae,

⇒ Area of cross-section of pipe × Velocity of flow = Volume of a tank upto water level in the tank 

⇒ 1.2 × 0.75 × 15000 × x = 180 × 140 × 4

⇒ x = \(\frac{1121}{5}\)  

⇒ x = 7 hours 28 minutes.

Therefore, the water level will rise by 4 m in 7 hours 28 minutes.