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Eight drops of water each radius 2mm are falling through the air at a terminal velocity of 8cm/s. If they coalesce to form a single drop, the terminal velocity of the combined drop will be:

Correct answer: D. 32cm/s

  • A. 8cm/s
  • B. 16cm/s
  • C. 24cm/s
  • D. 32cm/s

Explanation

Volume scales ∝ r³, combining 8 equal drops doubles the radius (since 8×r³ → (2r)³). Terminal velocity under Stokes- like scaling ∝ r², so Vₙₑw = (2²) V = 4×8 cm/s = 32 cm/s.

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About Fluid Dynamics

Fluid flow is described through speed, pressure and density, including steady flow and the equation of continuity for conserving mass. Bernoulli's equation relates pressure, speed and height, while fluid drag and terminal velocity explain why a falling object eventually moves at constant speed when drag balances its weight.

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