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NEET2026PhysicsChapterActual

A small solid sphere of density d is dropped into a tall cylinder containing a viscous liquid of density d 3 . After some time, the sphere reaches a constant terminal velocity. If the true weight of the sphere is W , what is the magnitude of the viscous drag force acting on it at this stage?

Options

  1. AW 3
  2. B2W 3
  3. CW
  4. D4W 3

Correct answer

B. 2W 3

Step-by-step solution

Let the volume of the sphere be V . The true weight of the sphere is given by W = V d g . The buoyant force acting on the sphere is F_B = V ( d 3 ) g = V d g 3 = W 3 . When the sphere reaches a constant terminal velocity, the net force acting on it is zero. The downward weight is balanced by the upward buoyant force and the viscous drag force F_v . W = F_B + F_v F_v = W - F_B F_v = W - W 3 = 2W 3 Answer: 2W 3

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