BHU PMT BHU PMT (Screening) Solved Paper-2011

  • question_answer
    A disk starts rotating from rest about its axis with an angular acceleration equal to\[a=10\] \[rad/{{s}^{2}}\]where t is time in second. At\[t=0\]disk is at rest. The time taken by disk to make its first complete revolution is

    A)  \[{{\left( \frac{6\pi }{5} \right)}^{1/3}}\]                              

    B)  \[{{\left( \frac{3\pi }{10} \right)}^{1/3}}\]

    C)  \[{{\left( \frac{2\pi }{5} \right)}^{1/2}}\]                              

    D)  \[{{\left( \frac{6\pi }{13} \right)}^{1/3}}\]

    Correct Answer: A

    Solution :

                     \[\frac{d\omega }{dt}=10t\] \[\int_{0}^{\omega }{d\omega }=\int_{0}^{t}{10}tdt\] \[\omega =5{{t}^{2}}\] \[\int_{0}^{2\pi }{d\theta }=\int_{0}^{{{t}_{0}}}{5}{{t}^{2}}dt\]                 \[2\pi \frac{5t_{0}^{3}}{3}\]                 \[{{t}_{0}}={{\left( \frac{6\pi }{5} \right)}^{1/3}}\]


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