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At a confluence, river Alaknanda (width 12 m, speed 20 km/h) meets river Bhagirathi (width 8 m, speed 16 km/h) to form river Ganga (width 16 m). The water depth is the same in all three rivers. Using continuity (conservation of volume flow), find the average speed of water in the Ganga.
- 23 km/h
- 46 km/h
- 20 km/h
- 40 km/h
Correct answer: 23 km/h
Solution
By continuity, total volume per unit time entering equals that leaving. With equal depth d, depth cancels and only width*speed products matter.
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