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Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2008

  • question_answer
    Spherical balls of radius R are falling in a viscous                 fluid of viscosity \[\eta \] with a velocity \[v.\] The retarding viscous force acting on the spherical       ball is            

    A)              directly proportional to R but inversely     proportional to \[v\]

    B)              directly proportional to both radius R and                velocity \[v\]

    C)              inversely proportional to R but directly     proportional to velocity \[v\]

    D)              inversely proportional to R but directly     proportional to velocity \[v\]

    Correct Answer: B

    Solution :

    Retarding force acting on a ball falling into a viscous fluid                                 \[F=6\pi \eta Rv\] where R = radius of ball, v = velocity of ball and    \[\eta =\] coefficient of viscosity \[\therefore \]  \[F\propto R\] and \[F\propto v\] Or in words, retarding force is directly proportional to both R and v.


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