RAJASTHAN PMT Rajasthan - PMT Solved Paper-2008

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

    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 :

                    \[x=\alpha \,\,{{t}^{3}},\,\,y=\beta {{t}^{3}}\]                 \[{{v}_{x}}=\frac{dx}{dt}=3\alpha {{t}^{2}}\]                 \[{{v}_{y}}=\frac{dy}{dt}=3\beta {{t}^{2}}\] 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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