J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    Two small spheres of radii r and \[4r\] fall through a viscous liquid with the same 'terminal velocity. The ratio between the viscous forces acting on them is

    A)  \[1:2\]           

    B)  \[4:1\]

    C)  \[1:16\]          

    D)  \[1:4\]

    Correct Answer: D

    Solution :

    The magnitude of the viscous force depends on the shape and size of the body, its speed and the viscosity of the fluid. Stokes established that if a sphere of radius r moves with velocity v through a fluid of viscosity y{, the viscous force opposing the motion of the sphere \[F=6\pi \eta rv\] \[\frac{{{F}_{1}}}{{{F}_{2}}}=\frac{{{r}_{1}}}{{{r}_{2}}}\] [As \[\eta =\] = constant and \[{{v}_{1}}={{v}_{2}}\]] \[\frac{{{F}_{1}}}{{{F}_{2}}}=\frac{r}{4r}\]


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