Water flows through a horizontal pipe of varying cross section. At point 1, diameter is 10 cm and velocity is 2.0 m/s. What is the flow velocity at point 2 where diameter is 5.0 cm?
Answer and explanation
Correct answer: B. 8.0 m/s
- Step 1: Continuity equation for incompressible fluid: A1 v1 = A2 v2. Step 2. Area ratio: A1 / A2 = (d1 / d2)^2 = (10 / 5)^2 = 2^2 = 4. Step 3. v2 = v1 (A1 / A2) = 2.0 4 = 8.0 m/s. Answer: 8.0 m/s. Why not the others: 4.0 m/s uses diameter ratio without squaring; 1.0 m/s inverts the ratio.
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