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A straight 100 m long raw water gravity main is to carry water from an intake structure to the jack well of a water treatment plant. The required flow through this water main is 0.21 m³/s. Allowable velocity through the main is 0.75 m/s. Assume f = 0.01, g = 9.81 m/s². The minimum gradient (in cm/100 m length) to be given to this gravity main so that the required amount of water flows without any difficulty is __________.
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- 4.8 cm
- 4.01 cm
- 5.8 cm
- 3.025 cm
Correct Option: A
4.7 to 4.9
Q = 0.21 m³/s
V = 0.75 m/s
| d² | |||
| 4 | V |
| ∴ | = 0.28 m² | |
| 0.75 |
∴ d = 0.597 m
| hf = | = | = 0.098m = 4.8 cm | ||
| 2gd | 2 × 9.81 × 0.597 |
| Minimum gradient = | = | ||
| l | 100 m |
∴ Answer is 4.8
