JEE MAIN - Physics (2023 - 29th January Evening Shift - No. 22)
A metal block of base area 0.20 m$$^2$$ is placed on a table, as shown in figure. A liquid film of thickness 0.25 mm is inserted between the block and the table. The block is pushed by a horizontal force of 0.1 N and moves with a constant speed. IF the viscosity of the liquid is $$5.0\times10^{-3}~\mathrm{Pl}$$, the speed of block is ____________ $$\times10^{-3}$$ m/s.
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Answer
25
Explanation
As the block moves with constant speed, the horizontal force is balanced by viscous force thus
$$F = \eta A{{\Delta v} \over {\Delta z}}$$
$$0.1 = 5 \times {10^{ - 3}} \times 0.2 \times {v \over {.25 \times {{10}^{ - 3}}}}$$
$$ \Rightarrow v = 25 \times {10^{ - 3}}$$ m/s
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