JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Afternoon)

  • question_answer
    A rectangular solid box of length 0.3 m is held horizontally, with one of its sides on the edge of a platform of height 5m. When released, it slips off the table in a very short time \[\tau =0.01s,\] remaining essentially horizontal. The angle by which it would rotate when it hits the ground will be (in radians) close to :- [JEE Main 8-4-2019 Afternoon]

    A) 0.02                

    B) 0.28

    C) 0.5      

    D)   0.3

    Correct Answer: C

    Solution :

    Angular impulse = change in angular momentum \[\tau \,\Delta t=\Delta L\] \[mg\frac{\ell }{2}\times .01=\frac{m{{\ell }^{2}}}{3}\omega \] \[\omega =\frac{3g\times 0.01}{2\ell }\] \[=\frac{3\times 10\times .01}{2\times 0.3}\] \[=\frac{1}{2}=0.5rad/s\] time taken by rod to hit the ground \[t=\sqrt{\frac{2h}{g}}=\sqrt{\frac{2\times 5}{10}}=1\sec .\] in this time angle rotate by rod \[\theta =\omega t=0.5\times 1=0.5\] radian


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