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MHT CET202523 Apr 2025Morning ShiftPhysicsMechanical Properties of FluidsActual

A disc of paper of radius ' R ' has a hole of radius ' r '. It is floating on a liquid of surface tension ' T '. The force of surface tension on the disc is

Options

  1. A2 ~T ( R - r )
  2. B2 ~T ( R + r )
  3. C3 ~T R
  4. D4 ~T ( R + r )

Correct answer

B. 2 ~T ( R + r )

Step-by-step solution

The force due to surface tension on a floating object equals the product of surface tension T and the total perimeter length L of liquid contact. For a disc with outer radius R and hole radius r , contact occurs along both circumferences: L = 2 R + 2 r = 2 (R + r) . The resulting force is F = T L = T 2 (R + r) = 2 T (R + r) . Final answer: B

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