BHU PMT BHU PMT (Screening) Solved Paper-2006

  • question_answer
    The displacement\[x\]of opal-tide varies with time t as\[x=a{{e}^{-\alpha t}}+b{{e}^{\beta t}}\]where a, b,\[\alpha \]and\[\beta \] are positive constants. The velocity of the particle will:

    A)  go on decreasing with time

    B)  be independent of\[\alpha \]and\[\beta \]

    C)  drop to zero when\[\alpha =\beta \]

    D)  go on increasing with time

    Correct Answer: D

    Solution :

                     Given, \[a=a{{e}^{-\alpha t}}+b{{e}^{\beta t}}\] So,          velocity \[v=\frac{dx}{dt}\]                 \[=-a\alpha {{e}^{-\alpha t}}+b\beta {{e}^{\beta t}}\]                 \[=A+B\] Where \[A=-a\alpha {{e}^{-\alpha t}},B=b\beta {{e}^{\beta t}}\]             The value of term\[A=-a\alpha {{e}^{-\alpha t}}\]decreases and of term\[B=b\beta {{e}^{\beta t}}\]increases with increase in time. As a result, velocity goes on increasing with time.


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