CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2011

  • question_answer
    A particle crossing the origin of co-ordinates at time t = 0, moves in the xy-plane with a constant acceleration a in the y-direction. If its equation of motion is \[y=b{{x}^{2}}\] (b is a constant), its velocity component in the x-direction is

    A) \[\sqrt{\frac{2b}{a}}\]                   

    B)        \[\sqrt{\frac{A}{2b}}\]                  

    C) \[\sqrt{\frac{a}{b}}\]                     

    D)        \[\sqrt{\frac{b}{a}}\]

    E) \[\sqrt{ba}\]

    Correct Answer: B

    Solution :

    \[y=b{{x}^{2}}\] \[\frac{dy}{dt}=2bx\frac{dx}{dt}\]                        ...(i)                 \[\frac{dy}{dt}=at\]            \[(\because {{v}_{y}}={{u}_{y}}+{{a}_{y}}t)\]                 \[at=2bx\frac{dx}{dt}\]                 \[atdt=2bx\,dx\] Take integration of both sides                 \[\int{atdt}=\int{2bx}\,dx\]                 \[\frac{a{{t}^{2}}}{2}=b{{x}^{2}}+c\]                       ...(ii) At           \[t=0,\text{ }x=0\]                 \[c\Rightarrow 0\] Then,    \[\frac{a{{t}^{2}}}{2}=b{{x}^{2}}\]                 \[x=\sqrt{\frac{a{{t}^{2}}}{2b}}=t\sqrt{\frac{a}{2b}}\] \[\therefore \]  \[{{v}_{x}}=\frac{dx}{dt}=\sqrt{\frac{a}{2b}}\]


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