J & K CET Engineering J and K - CET Engineering Solved Paper-2003

  • question_answer
    The velocity of a small ball of mass M and density \[{{d}_{1}}\] when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is \[{{d}_{2}},\] the viscous force acting on the ball is

    A)  \[Mg\left( 1-\frac{{{d}_{2}}}{{{d}_{1}}} \right)\]

    B)  \[Mg\frac{{{d}_{1}}}{{{d}_{2}}}\]

    C)  \[Mg({{d}_{1}}-{{d}_{2}})\]

    D)  \[Mg{{d}_{1}}{{d}_{2}}\]

    Correct Answer: A

    Solution :

    At terminal velocity is the speed at which the gravitational force pulling it downwards is equal and opposite to the atmospheric drag, at this speed the object ceases to accelerate down- wards and falls at constant speed. \[\therefore \] Viscous force upwards = Apparent weight in liquid \[\therefore \] Viscous force \[=Mg-\frac{Mg{{d}_{2}}}{{{d}_{1}}}\] Viscous force \[=Mg\left( 1-\frac{{{d}_{2}}}{{{d}_{1}}} \right)\]


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