Uttarakhand PMT Uttarakhand PMT Solved Paper-2009

  • question_answer
    A body executes simple harmonic motion under the action of force F1 with a time period \[\frac{3}{5}s.\] If the force is changed to\[{{F}_{2}}\]it executes  simple harmonic motion with time period \[\frac{3}{4}s.\] If both forces \[{{F}_{1}}\]and\[{{F}_{2}}\]act simultaneously in the same direction on the body, its time period will

    A)  \[\frac{12}{25}s.\]         

    B)  \[\frac{24}{25}s.\]

    C)  \[\frac{24}{25}s.\]        

    D)  \[\frac{15}{12}s.\]

    Correct Answer: A

    Solution :

     Under the influence of one force\[{{F}_{1}}=m\omega _{1}^{2}y\] and under the action of another force, \[{{F}_{2}}=m\omega _{2}^{2}y\] Under the action of both the forces\[F={{F}_{1}}+{{F}_{2}}\] \[\Rightarrow \] \[m{{\omega }^{2}}y=m\omega _{1}^{2}y+m\omega _{2}^{2}y\] \[\Rightarrow \] \[{{\omega }^{2}}=\omega _{1}^{2}+\omega _{2}^{2}\] \[\Rightarrow \] \[{{\left[ \frac{2\pi }{T} \right]}^{2}}={{\left[ \frac{2\pi }{{{T}_{1}}} \right]}^{2}}+{{\left[ \frac{2\pi }{{{T}_{2}}} \right]}^{2}}\] \[\Rightarrow \] \[T=\sqrt{\frac{T_{1}^{2}\times T_{2}^{2}}{T_{1}^{2}+T_{2}^{2}}}\] \[=\sqrt{\frac{{{\left( \frac{4}{5} \right)}^{2}}{{\left( \frac{3}{5} \right)}^{2}}}{{{\left( \frac{4}{5} \right)}^{2}}+{{\left( \frac{3}{5} \right)}^{2}}}}\] \[=\frac{12}{25}s\]


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