Q101 / 125 · BITSAT 2010 · Physics

Two circular plates of radius $5 \mathrm{~cm}$ each, have a 0.01 mm thick water film between them. Then what will be the force required to separate these plate (S.T. of water $=73$ dyne/cm)?

  • A
    $125 \mathrm{~N}$
  • B
    $95 \mathrm{~N}$
  • Correct answer
    C
    $115 \mathrm{~N}$
  • D
    $105 \mathrm{~N}$

Solution

$\begin{aligned} \mathrm{F}=& \frac{2 \mathrm{AT}}{\mathrm{d}}=\frac{2 \times \pi \times(0.05)^{2} \times 73 \times 10^{-3}}{0.01 \times 10^{-3}} \\=& 36.5 \pi \approx 115 \text { newton } \end{aligned}$

Hence, the correct answer is option: 'C'.

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