JEE Main & Advanced Mathematics Differential Equations Question Bank Formation of differential equations

  • question_answer
    The differential equation of displacement of all "Simple harmonic motions" of given period \[2\pi /n\], is

    A)                 \[\frac{{{d}^{2}}x}{d{{t}^{2}}}+nx=0\]  

    B)                 \[\frac{{{d}^{2}}x}{d{{t}^{2}}}+{{n}^{2}}x=0\]

    C)                 \[\frac{{{d}^{2}}x}{d{{t}^{2}}}-{{n}^{2}}x=0\] 

    D)                 \[\frac{{{d}^{2}}x}{d{{t}^{2}}}+\frac{1}{{{n}^{2}}}x=0\]

    Correct Answer: B

    Solution :

                       The displacement of x for all S.H.M. is given by \[x=a\cos (nt+b)\]Þ\[\frac{dx}{dt}=-na\sin (nt+b)\]         Þ \[\frac{{{d}^{2}}x}{d{{t}^{2}}}=-{{n}^{2}}a\cos (nt+b)\] Þ \[\frac{{{d}^{2}}x}{d{{t}^{2}}}=-{{n}^{2}}x\]                 Þ \[\frac{{{d}^{2}}x}{d{{t}^{2}}}+{{n}^{2}}x=0\].


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