JCECE Engineering JCECE Engineering Solved Paper-2015

  • question_answer
    The amplitude of a wave disturbance propagating in the positive \[X-\]direction is given by \[y=\frac{1}{2+{{x}^{2}}}\]at\[t=0\]and\[y=\frac{1}{[2+{{(x-1)}^{2}}]}\]at \[t=3s\], where x and y are in metre. If the shape of the wave disturbance does not change during the propagation, the velocity of the wave is

    A) \[\frac{1}{2}m{{s}^{-1}}\]                            

    B) \[\frac{1}{3}m{{s}^{-1}}\]

    C) \[\frac{1}{4}m{{s}^{-1}}\]                            

    D)  \[\frac{1}{5}m{{s}^{-1}}\]

    Correct Answer: B

    Solution :

    At\[t=0,\,\,y=\frac{1}{2+{{x}^{2}}}\] or            \[2y+y{{x}^{2}}=1\] or            \[y{{x}^{2}}=+1-2y\] or            \[x=\sqrt{\frac{1-2y}{y}}={{x}_{1}}\]       (say) At\[t=3\,\,s\],   \[y=\frac{1}{[2+{{(x-1)}^{2}}]}\] or            \[2+{{(x-1)}^{2}}=\frac{1}{y}\] or            \[{{(x-1)}^{2}}=\frac{1}{y}-2=\frac{1-2y}{y}\] or            \[x=1+\sqrt{\frac{1-2y}{y}}={{x}_{2}}\] \[\therefore \]\[v=\frac{{{x}_{2}}-{{x}_{1}}}{{{t}_{2}}-{{t}_{1}}}=\frac{1+\sqrt{\frac{1-2y}{y}}-\sqrt{\frac{1-2y}{y}}}{3-1}=\frac{1}{3}m{{s}^{-1}}\]


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