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Water flows steadily through a tube of varying cross-section. At sections A, B and C the cross-sectional areas are 25 cm², 15 cm² and 35 cm² respectively. Find the ratio of water speeds at A: B: C.
- 5: 3: 7
- 7: 3: 5
- 21: 35: 15
- 1: 1: 1
Correct answer: 21: 35: 15
Solution
Continuity: A*v is constant, so v ratio = (1/25): (1/15): (1/35). Multiply each by the common factor 525 (LCM): (525/25): (525/15): (525/35) = 21: 35: 15.
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