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


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