AFMC AFMC Solved Paper-2002

  • question_answer
    The displacement of a particle moving in a straight line depends on lime as  \[x=\alpha {{t}^{3}}+\beta {{t}^{2}}+\gamma t+\delta \] The ratio of initial acceleration to its initial velocity depends:

    A) only on \[\alpha \] and \[\beta \]            

    B) only on \[\beta \] and \[\gamma \]

    C) only on \[\alpha \] and \[\beta \]            

    D)  only on \[\alpha \]

    Correct Answer: B

    Solution :

    Key Idea: Rate of change of displacement is velocity and rate of change of velocity is acceleration. The given equation for displacement is \[x=\alpha {{t}^{3}}+\beta {{t}^{3}}+\gamma t+\delta \] We know that velocity \[=\frac{dx}{dt}\] \[\therefore \]    \[v=\frac{dx}{dt}=3{{t}^{2}}\alpha +2t\beta +\gamma \]  Initial velocity when t = 0, is \[{{v}_{0}}=3\alpha \times 0+2\beta \times 0+\gamma =\gamma \]               ?(i) Also acceleration \[=\frac{dv}{dt}\] \[\therefore \]     \[a=\frac{dv}{dt}=\frac{{{d}^{2}}x}{d{{t}^{2}}}=6\,t\,\alpha +2\beta \] Initial acceleration when t = 0, is \[{{a}_{o}}=6\,t\times 0+2\beta =2\beta \]        ?(ii) Ratio of initial acceleration to initial velocity is \[\frac{{{a}_{o}}}{{{v}_{o}}}=\frac{2\beta }{\gamma }\] which shown that this ratio depends only on\[\beta \]and \[\gamma \].


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