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Two fog droplets have radii 2:3, their terminal velocities are

Correct answer: B. 4:9

  • A. 4:6
  • B. 4:9
  • C. 2:9
  • D. 4:3

Explanation

The formula for terminal velocity is vt= 2gr2 ρ/9ηSince the terminal velocity vt is proportional to the square of the radius ( r2 ) the ratio of their terminal velocities will be the square of the ratio of their radii. Given the ratio of radii as 2:3, the square of this ratio is ( 2 / 3 )2 = 4 / 9. Therefore, the ratio of their terminal velocities will be 4:9

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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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