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JEE Main & Advanced JEE Main Online Paper (Held On 23 April 2013)

  • question_answer
                    A particle of mass 2 kg is moving such hat at time t, its position, in meter, is given by \[\overset{\to }{\mathop{\operatorname{r}}}\,(\operatorname{t})=5\hat{i}-2{{\operatorname{t}}^{2}}\hat{j}.\]The angular momentum of the particle at \[\operatorname{t}=2s\] about the origin in kg \[{{\operatorname{m}}^{-2}}\]\[{{\operatorname{s}}^{-2}}\] is :     [JEE Main Online Paper ( Held On 23  April 2013 )

    A) \[-80\hat{k}\]

    B)                        \[\left( 10\hat{i}-16\hat{j} \right)\]

    C)                        \[-40\hat{k}\]                   

    D)                        \[40\hat{k}\]­­

    Correct Answer: A

    Solution :

      Angular momentum \[L=m(v\times r)\] \[2kg\left( \frac{dr}{dt}\times r \right)=2kg(4tj\times 5i-2{{t}^{2}}\hat{j})\]  \[=2kg(-20t\hat{k})=2kg\times -20\times 2{{m}^{-2}}{{s}^{-1}}\hat{k}\]\[=-80\hat{k}\]


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