NEET Physics NLM, Friction, Circular Motion NEET PYQ-NLM Friction Circular Motion

  • question_answer
    A ball of mass 0.25 kg attached to the end of a string of length 1.96 m is moving in a horizontal circle. The string will break if the tension is more than 25 N. What is the maximum speed with which the ball can be moved?    [AIPMT 1998]

    A) 14 m/s

    B) 3 m/s

    C) 3.92 m/s

    D) 5 m/s

    Correct Answer: A

    Solution :

    Key Idea: In a horizontal circle, tension in the string provides the necessary centripetal force. For a ball to move in horizontal circle, the ball should satisfied the condition:
                Tension in the string = Centripetal force
    \[\Rightarrow \]   \[{{T}_{\max }}=\frac{M{{v}^{2}}_{\max }}{R}\]
    \[\Rightarrow \]   \[{{v}_{\max }}=\sqrt{\frac{{{T}_{\max }}.R}{M}}\]                            …(i)
                Making substitution, we obtain
                            \[{{v}_{\max }}=\sqrt{\frac{25\times 1.96}{0.25}}\]
                            \[=\sqrt{196}\]
                            \[=14\,m/s\]
    Note:    In a vertical circle, the tension at the highest point in zero and at lowest pint is maximum.


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