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JEE Main & Advanced Physics Vectors Question Bank Multiplication of Vectors

  • question_answer
    The position of a particle is given by \[\overrightarrow{r}=(\overrightarrow{i}+2\overrightarrow{j}-\overrightarrow{k})\] momentum \[\overrightarrow{P}=(3\overrightarrow{i}+4\overrightarrow{j}-2\overrightarrow{k}).\]The angular momentum is perpendicular to                         [EAMCET (Engg.) 1998]

    A)                 x-axis

    B)                 y-axis

    C)                 z-axis    

    D)                 Line at equal angles to all the three axes

    Correct Answer: A

    Solution :

                        \[\vec{L}=\vec{r}\times \vec{p}=\left| \,\begin{matrix}    {\hat{i}} & {\hat{j}} & {\hat{k}}  \\    1 & 2 & -1  \\    3 & 4 & -2  \\ \end{matrix}\, \right|\]\[=-\hat{j}-2\hat{k}\] i.e. the angular momentum is perpendicular to x-axis.   


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