JEE Main & Advanced Physics Wave Mechanics Question Bank Vibration of String

  • question_answer
    A sonometer wire resonates with a given tuning fork forming standing waves with five antinodes between the two bridges when a mass of 9 kg is suspended from the wire. When this mass is replaced by a mass M, the wire resonates with the same tuning fork forming three antinodes for the same positions of the bridges. The value of M is  [IIT-JEE (Screening) 2002]

    A)            25 kg                                       

    B)            5 kg

    C)            12.5 kg                                    

    D)            1/25 kg

    Correct Answer: A

    Solution :

                         The frequency of vibration of a string \[n=\frac{p}{2l}\sqrt{\frac{T}{m}}\] Also number of loops = Number of antinodes. Hence, with 5 antinodes and hanging mass of 9 kg. We have p = 5 and T = 9g Þ \[{{n}_{1}}=\frac{5}{2l}\sqrt{\frac{9g}{m}}\] With 3 antinodes and hanging mass M We have p = 3 and T = Mg Þ \[{{n}_{2}}=\frac{3}{2l}\sqrt{\frac{Mg}{m}}\] \[\because \]   n1 = n2 Þ \[\frac{5}{2l}\sqrt{\frac{9g}{m}}=\frac{3}{2l}\sqrt{\frac{Mg}{m}}\]Þ \[M=25\] kg.


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