J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    Two   pendulums   begin   to   swing simultaneously. If the ratio of the frequency of oscillations of the two is \[7:8,\] then the ratio of lengths of the two pendulums will be

    A)  \[7:8\]        

    B)  \[8:7\]

    C)  \[49:64\]      

    D)  \[64:49\]

    Correct Answer: D

    Solution :

    The frequency of oscillation of pendulum of length l, is given by \[n=\frac{1}{2\pi }\sqrt{\frac{g}{l}}\] Given, \[{{n}_{1}}:{{n}_{2}}=7:8,\] then \[\frac{{{n}_{1}}}{{{n}_{2}}}=\sqrt{\frac{{{l}_{2}}}{{{l}_{1}}}}\] \[\Rightarrow \] \[\frac{7}{8}=\sqrt{\frac{{{l}_{2}}}{{{l}_{1}}}}\] On squaring \[\Rightarrow \] \[\frac{{{l}_{1}}}{{{l}_{2}}}=\frac{64}{49}\]


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