KVPY Sample Paper KVPY Stream-SX Model Paper-31

  • question_answer
    A particle moves in the x-y plane with velocity \[\overrightarrow{v}=a\overset{\hat{\ }}{\mathop{i}}\,+bt\overset{\hat{\ }}{\mathop{j}}\,\].At the instant \[t=\frac{a\sqrt{3}}{b}\]the magnitudes  of tangential, normal and total accelerations are:

    A) \[\frac{\sqrt{3}}{2}b,\,\,\frac{b}{2}\]and b respectively

    B) \[\frac{b}{2},\,\,\frac{b}{2}\]and b respectively

    C) \[\sqrt{2}b,\,\,\sqrt{2}b\]and b respectively

    D) none of the above

    Correct Answer: A

    Solution :

    \[\overrightarrow{v}=a\overset{\hat{\ }}{\mathop{j}}\,+bt\overset{\hat{\ }}{\mathop{j}}\,;\,\]\[\therefore \,\,\,\,\,\,\overrightarrow{a}=b\overset{\hat{\ }}{\mathop{j}}\,\];
    Total acceleration =b; speed, \[v={{\left( {{a}^{2}}+{{b}^{2}}{{t}^{2}} \right)}^{1/2}}\]
    Tangential acceleration
    \[=\frac{dv}{dt}=\frac{1}{2}{{\left( {{a}^{2}}+{{b}^{2}}{{t}^{2}} \right)}^{-1/2}}\left( 2{{b}^{2}}t \right)\]
    At\[\,\,\,\,t=\frac{\sqrt{3a}}{b}\]; Tangential acceleration\[t=\frac{\sqrt{3}b}{2}\] and normal acceleration \[=\sqrt{{{b}^{2}}-\frac{3{{b}^{2}}}{4}}=\frac{b}{2}\]


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