Multiple choice

The water in a rectangular reservoir having a base 90 m by 50 m is 4.5 m deep. In what time can the water be emptied by a pipe of which the cross-section is a square of side 24 cm, if the water runs through the pipe at the rate of 9 km per hour?

  1. 40 hrs.

  2. 58 hrs.

  3. 54 hrs.

  4. 52 hrs.

  5. None of these
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The volume of the reservoir is 90 × 50 × 4.5 = 20,250 m³. The pipe cross-sectional area is 0.24 × 0.24 = 0.0576 m². Water flows at 9 km/hr = 9,000 m/hr, so flow rate = 0.0576 × 9,000 = 518.4 m³/hr. Time = 20,250 ÷ 518.4 = 39.06 hours. This rounds to ~39 hours, not 40 exactly, so 'None of these' is correct.

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