JEE Main & Advanced AIEEE Solved Paper-2006

  • question_answer
    If the terminal speed of a sphere of gold (density\[=19.5\text{ }kg/{{m}^{3}}\]) is 0.2 m/s in a viscous liquid (density\[=1.5\text{ }kg/{{m}^{3}}\]), find the terminal speed of a sphere of silver (density =10.5\[kg/{{m}^{3}}\]) of the same size in the same liquid.     AIEEE  Solved  Paper-2006

    A) 0.4 m/s        

    B)       0.133 m/s           

    C)        0.1 m/s          

    D)        0.2 m/s

    Correct Answer: C

    Solution :

    Terminal speed of spherical body in a viscous liquid is given by \[{{v}_{T}}=\frac{2{{r}^{2}}(\rho -\sigma )g}{9\eta }\] \[\Rightarrow \] \[{{v}_{T}}\propto (\rho -\sigma )\] where,\[\rho =\]density of substance of body \[\sigma =\]density of liquid. Thus, from given data \[\frac{{{v}_{T}}(Ag)}{{{v}_{T}}(Gold)}=\frac{{{\rho }_{Ag}}-{{\sigma }_{l}}}{{{\rho }_{Gold}}-{{\sigma }_{l}}}\] \[\Rightarrow \]\[{{v}_{T}}(Ag)=\frac{10.5-1.5}{19.5-1.5}\times 0.2\] \[=\frac{9}{18}\times 0.2\] \[=0.1\text{ }m/s\]


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