NEET Sample Paper NEET Sample Test Paper-68

  • question_answer
    Two simple pendulums first of bob mass \[{{M}_{1}}\] and length \[{{L}_{1}}\] second of bob mass \[{{M}_{2}}\] and length \[{{L}_{2}}\] \[{{M}_{1}}={{M}_{2}}\,\,and\,\,{{L}_{1}}=2{{L}_{2}}\]. If the vibrational energy of both is same. Then which is correct?

    A) Amplitude of B greater than A  

    B) Amplitude of B smaller than A         

    C) Amplitudes will be same             

    D) None of these                      

    Correct Answer: B

    Solution :

    \[n=\frac{1}{2\pi }\,\sqrt{\frac{g}{l}}\,\,\,\,\Rightarrow \,\,n\propto \frac{1}{\sqrt{l}}\] \[\Rightarrow \,\,\,\frac{{{n}_{1}}}{{{n}_{2}}}\,\,=\,\,\sqrt{\frac{{{l}_{2}}}{{{l}_{1}}}}\,\,=\,\,\sqrt{\frac{{{L}_{2}}}{2{{L}_{2}}}}\] \[\Rightarrow \,\,\,\,\frac{{{n}_{1}}}{{{n}_{2}}}\,\,=\,\frac{1}{\sqrt{2}}\,\,\Rightarrow \,\,{{n}_{2}}\,=\,\sqrt{2}{{n}_{1}}\,\,\Rightarrow \,{{n}_{2}}>{{n}_{1}}\] Energy \[E=\frac{1}{2}m{{\omega }^{2}}{{a}^{2}}=2{{\pi }^{2}}m{{n}^{2}}{{a}^{2}}\] \[\Rightarrow \,\,\,\frac{a_{1}^{2}}{a_{2}^{2}}\,\,=\,\,\frac{{{m}_{2}}n_{2}^{2}}{{{m}_{1}}n_{1}^{2}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(\because \,\,\,\,\,E\,\,is\,\,same)\] \[Given\,\,{{n}_{2}}>{{n}_{1}}\,and\,\,{{m}_{1}}={{m}_{2}}\,\,\Rightarrow \,\,{{a}_{1}}>{{a}_{2}}\]


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