NEET Physics Simple Harmonic Motion NEET PYQ-Simple Harmonic Motion

  • question_answer
    A mass m is vertically suspended from a spring of negligible mass; the system oscillates with a frequency n. What will be the frequency of the system, if a mass 4 m is suspended from the same spring?                                       [AIPMT 1998]

    A)  \[\frac{n}{4}\] 

    B)       4n                   

    C)  \[\frac{n}{2}\] 

    D)                   2 n

    Correct Answer: C

    Solution :

    Key Idea: Time period of oscillating system whether it is a simple pendulum of spring-mass system, is given by
                            \[T=2\pi \sqrt{\left( \frac{displacement}{acceleration} \right)}\]
                Time period of spring-mass system is
                            \[n=\frac{1}{T}=\frac{1}{2\pi }\sqrt{\frac{acceleration}{displacement}}\]
                            \[n=\frac{1}{2\pi }\sqrt{\frac{g}{l}}\]                             ....(i)
                In case of vertical spring mass system, in equilibrium position
                            \[kl=mg\Rightarrow \frac{g}{l}=\frac{k}{m}\]
                where \[l=\] extension in the spring and
                \[k=\] spring constant or force constant of spring
                \[\therefore \,\]  From Eq. (i), we have
                            \[n=\frac{1}{2\pi }\sqrt{\frac{k}{m}}\]
    or         \[n\propto \,\,\frac{1}{\sqrt{m}}\]
    or         \[\frac{{{n}_{1}}}{{{n}_{2}}}=\sqrt{\frac{{{m}_{2}}}{{{m}_{1}}}}\]
    but        \[{{m}_{1}}=m,\text{ }{{m}_{2}}=4m\text{ };\text{ }{{n}_{1}}=n\](given)
    \[\therefore \]    \[\frac{n}{{{n}_{2}}}=\sqrt{\frac{4m}{m}}=2\]
    or         \[{{n}_{2}}=\frac{n}{2}\]


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