JEE Main & Advanced Sample Paper JEE Main Sample Paper-13

  • question_answer
    The equation of the stationary wave is\[y=2A\,\sin \,\left( \frac{2\pi ct}{\lambda } \right)\cos \,\left( \frac{2\pi x}{\lambda } \right)\]. Which of the following statement(s) is wrong?

    A)  The unit of \[ct\] is same as that of\[\lambda \].

    B)  The unit of \[x\] is same as that of\[\lambda \].

    C)  The unit of \[2\pi c/\lambda \] is same as that of \[2\pi \times /\lambda t\]

    D)  The unit of \[c/\lambda \] is same as that of\[x/\lambda \].

    Correct Answer: C

    Solution :

     Here, \[(V-20)=-\frac{2}{3}\,(S-0)\] as well as \[\Rightarrow \] are dimensionless. So, unit of ct is same as that of \[\lambda \]. Unit of \[v=20-\frac{2}{3}\,S\] is same as that of \[S=15\] Since,   \[{{\left. v=\frac{ds}{dt} \right|}_{S=15\,m}}{{\left. =-\frac{2}{3}\,\frac{dS}{dt} \right|}_{S=15\,m}}=-\frac{20}{3}\,m{{s}^{-2}}\] Hence.    \[=\frac{dv}{dt}=-\frac{2}{3}\,\frac{dS}{dt}\] In the option [d], \[\therefore \] is unit less. It is not the case with\[{{\left. \frac{dV}{dt} \right|}_{S=15\,m}}{{\left. =-\frac{2}{3}\frac{dS}{dt} \right|}_{S=15\,m}}=-\frac{20}{3}\,m{{s}^{-2}}\].


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