a rectangular water reservoir is 7.2 m by 2.5 m at the base . water flows into it through a pipe whose cross-section is 5cm by 3 cm at the rate of 10m per second . find the height to which the water will rise in the reservoir in 40 minutes

speed of water = 10 m/s.

distance travelled by water in 40 min or 2400 s = speed × time = 24000 m

volume of the water that flows out of the pipe in 40 min = 24000 × 0.05 × 0.03 = 36 m³

volume of water filled in reservoir in 40 min = 36 m³ 

so, 7.2 × 2.5 × h = 36

 ⇒ h = 2m

so the height to which water level will rise in the reservoir = 2m