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Water is flowing continuously from a tap having an internal diameter 8 × 10⁻³ m. The water velocity as it leaves the tap is 0.4 m s⁻¹. The diameter of the water stream at a distance 2 × 10⁻¹ m below the tap is close to:
- 7.5 × 10⁻³ m
- 9.6 × 10⁻³ m
- 3.6 × 10⁻³ m
- 5.0 × 10⁻³ m
Correct answer: 3.6 × 10⁻³ m
Solution
Speed after falling 0.2 m: v2 = sqrt(v1^2 + 2 g h) = sqrt(0.16 + 4) = 2.04 m/s. Continuity A1 v1 = A2 v2 gives d2 = d1*sqrt(v1/v2) = 8e-3*sqrt(0.4/2.04) ~ 3.6e-3 m.
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