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CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    The position of a particle is given by \[\overrightarrow{r}=\hat{i}+2\hat{j}-\hat{k}\]and its linear momentum is given by\[\overrightarrow{P}=3\hat{i}+4\hat{j}-2\hat{k}\]. Then its angular momentum,   about   the   origin   is perpendicular to

    A)  \[yz-\]plane                     

    B)  \[z-\]axis           

    C)  \[y-\]axis           

    D)        \[x-\]axis

    E)  \[xz-\]plane

    Correct Answer: D

    Solution :

    \[\overrightarrow{L}=\overrightarrow{r}\times \overrightarrow{P}=\left| \begin{matrix}    {\hat{i}} & {\hat{j}} & {\hat{k}}  \\    1 & 2 & -1  \\    3 & 4 & -2  \\ \end{matrix} \right|\] \[\overrightarrow{L}=\hat{i}(-4+4)-\hat{j}(-2+3)+\hat{k}(4-6)\]                 \[=-\hat{j}-2\hat{k}\] \[\overrightarrow{L}\]has components along -y axis and\[-z\]axis. The angular momentum is in y-z plane ie, perpendicular to\[x-\]axis


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