NEET Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन NEET PYQ-Fluid Mechanics, Surface Tension and Viscosity

  • question_answer
    A small sphere of radius 'r' falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to                               [NEET - 2018]

    A)  \[{{\text{r}}^{\text{5}}}\]                  

    B)       \[{{\text{r}}^{\text{2}}}\]

    C)  \[{{\text{r}}^{\text{3}}}\]                  

    D)       \[{{\text{r}}^{\text{4}}}\]

    Correct Answer: A

    Solution :

    [a] Power \[\text{=6}\pi \eta r{{V}_{T}}\cdot {{V}_{T}}=6\pi \eta rV_{T}^{2}\]
    \[{{V}_{T}}\propto {{r}^{2}}\]
    \[\Rightarrow \,\,\text{Power }\propto {{\text{r}}^{5}}\]

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