JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2004

  • question_answer
        The maximum and minimum tensions in the string whirling in a circle of radius 2.5 m are in the ratio 5:3 then its velocity is :

    A)  \[\sqrt{3}:1\]

    B)  7 m/s

    C)  \[1:\sqrt{3}\]

    D)  \[7.9\times {{10}^{4}}K\]

    Correct Answer: A

    Solution :

                    Minimum tension \[\frac{3}{2}KT=10.2\times 1.6\times {{10}^{-19}}J\] Maximum tension \[T=\frac{2}{3}\times \frac{10.2\times 1.6\times {{10}^{-19}}}{K}\] Let          \[=\frac{2}{3}\times \frac{10.2\times 1.6\times {{10}^{-19}}}{1.38\times {{10}^{-23}}}\] So,          \[=7.9\times {{10}^{4}}K\]                            ...(1) \[\upsilon =400m/s,r=160m,a=?\]                            ...(2) Dividing equation (1) by (2) \[F=\frac{m{{\upsilon }^{2}}}{r}\] \[ma=\frac{m{{\upsilon }^{2}}}{r}\] \[a=\frac{{{\upsilon }^{2}}}{r}\]                 Or           \[a=\frac{{{(400)}^{2}}}{160}=\frac{16\times {{10}^{4}}}{160}\]                 i.e.,        \[={{10}^{3}}m/{{s}^{2}}=1km/{{s}^{2}}\] \[{{T}_{1}}=\frac{m{{\upsilon }^{2}}}{r}-mg\]      \[{{T}_{2}}=\frac{m{{\upsilon }^{2}}}{r}+mg\] Or           \[\frac{m{{\upsilon }^{2}}}{r}=x\] Or           \[{{T}_{1}}=x-mg\]                 \[{{T}_{2}}=x+mg\]        


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