JEE Main & Advanced Sample Paper JEE Main Sample Paper-42

  • question_answer
    A uniform slender rod 1m long is initially standing vertically on a smooth, horizontal surface. It is struck by a sharp horizontal blow at the top end, with the blow directed at right angles to the rod axis. As a result, the rod acquires an angular velocity of 3.00 rad/s. What is the translational velocity of the centre of mass of the rod after the blow?

    A)  0.25 m/s                     

    B)  0.64 m/s

    C)  0.5 m/s                       

    D)  1.2 m/s

    Correct Answer: C

    Solution :

    Let the magnitude of the impulse delivered by the blow be represented by p. From the translational and rotational forms of Newton's second law\[{{v}_{c}}=\frac{p}{M}\]and \[{{I}_{c}}{{\omega }_{c}}=\frac{pl}{2}.\] Here, \[{{v}_{c}}\]is the rightward velocity of the centre of mass after the blow and \[{{\omega }_{c}}\]is the (positive clockwise) angular velocity of the rod after the blow about the point C. Using the fact that \[{{I}_{c}}=\frac{{{(Ml)}^{2}}}{12},\] we find that \[{{\omega }_{c}}l=\frac{6p}{M}.\]Therefore,\[{{v}_{c}}=\frac{({{\omega }_{c}}l)}{6}\] Since, \[{{\omega }_{c}}=3.00\,\text{rad/s}\]and l = 1.00 m, we find\[{{v}_{c}}=0.5\,\text{m/s}\].


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