JEE Main & Advanced Sample Paper JEE Main - Mock Test - 38

  • question_answer
    A particle is moving in a circle of radius R in such a way that at any instant the total acceleration makes an angle of \[45{}^\circ \] with radius. Initial speed of particle is\[{{v}_{0}}\]. The time taken to complete the first revolution is

    A) \[\frac{R}{{{v}_{0}}}{{e}^{-2\pi }}\]              

    B)        \[\frac{R}{{{v}_{0}}}(1-{{e}^{-2\pi }})\]

    C) \[\frac{R}{{{v}_{0}}}\]                  

    D)        \[\frac{2R}{{{v}_{0}}}\]

    Correct Answer: B

    Solution :

    [b] Total acceleration makes an angle of \[45{}^\circ \] with radius, i.e., tangential acceleration = radial acceleration or         \[R\alpha =R{{\omega }^{2}}\] or         \[\alpha ={{\omega }^{2}}\] or         \[\frac{d\omega }{dt}={{\omega }^{2}},\]      or     \[\frac{d\omega }{{{\omega }^{2}}}=dt\] i.e.        \[\int\limits_{{{\omega }_{0}}}^{\omega }{\frac{d\omega }{{{\omega }^{2}}}}=\int\limits_{0}^{t}{dt},\] or  \[\omega =\frac{{{\omega }_{0}}}{1-{{\omega }_{0}}t}\] or         \[\frac{d\theta }{dt}\frac{{{\omega }_{0}}}{1-{{\omega }_{0}}t},\] or    \[\int\limits_{0}^{2\pi }{d\theta }=\int\limits_{0}^{t}{\frac{{{\omega }_{0}}dt}{1-{{\omega }_{0}}t}}\] i.e.        \[t=\frac{1}{{{\omega }_{0}}}(1-{{e}^{-2\pi }})\]         \[\left( {{\omega }_{0}}=\frac{{{v}_{0}}}{R} \right)\] or         \[t=\frac{R}{{{v}_{0}}}(1-{{e}^{-2\pi }})\]


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