JEE Main & Advanced Physics Two Dimensional Motion JEE PYQ - Two Dimensional Relative Motion

  • question_answer
    The coordinates of a moving particle at any time t are given by \[x=\alpha {{t}^{3}}\] and \[y=\beta {{t}^{3}}\]. The speed of the particle at time t is given by [AIEEE 2003]

    A) \[3t\,\sqrt{{{\alpha }^{2}}+{{\beta }^{2}}}\]

    B) \[3{{t}^{2}}\,\sqrt{{{\alpha }^{2}}+{{\beta }^{2}}}\]

    C) \[{{t}^{2}}\,\sqrt{{{\alpha }^{2}}+{{\beta }^{2}}}\]

    D) \[\sqrt{{{\alpha }^{2}}+{{\beta }^{2}}}\]      

    Correct Answer: B

    Solution :

    [b] The positions of particle is given
                            \[x=\alpha {{t}^{3}},y=\beta {{t}^{3}}\]
    On differentiating with respect to t, we get
                \[{{v}_{x}}=\frac{dx}{dt}=3\alpha {{t}^{2}},{{v}_{y}}=\frac{dy}{dt}=3\beta {{t}^{2}}\]
    Resultant velocity
                                        \[v=\sqrt{{{v}_{x}}^{2}+{{v}_{y}}^{2}}\]
                                        \[=\sqrt{9{{\alpha }^{2}}{{t}^{4}}+9{{\beta }^{2}}{{t}^{4}}}\]
                                        \[=3{{t}^{2}}\sqrt{{{\alpha }^{2}}+{{\beta }^{2}}}\]


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