J & K CET Engineering J and K - CET Engineering Solved Paper-2006

  • question_answer
    The length of the projection of the line segment joining \[(3,-1,0)\] and \[(-3,5,\sqrt{2})\] on a line with direction cosines \[1/2,\,\,1/2,\,\,1/\sqrt{2}\] is

    A)  \[1\]                                           

    B)  \[2\]

    C)  \[3\]

    D)  \[4\]

    Correct Answer: A

    Solution :

    Projection of \[\vec{A}=3\hat{i}-\hat{j},\] Projection of  \[\vec{B}=-3\hat{i}+5\hat{j}+\sqrt{2}\hat{k}\] \[\therefore \] \[\overrightarrow{AB}=-6\hat{i}+6\hat{j}+\sqrt{2}\hat{k}\] Let \[\overrightarrow{CD}=\hat{i}/2+\hat{j}/2+\hat{k}/\sqrt{2}\] Now, Projection of \[\overrightarrow{AB}\] on \[\overrightarrow{CD}=\frac{\overrightarrow{AB}.\overrightarrow{CD}}{|\overrightarrow{CD}|}\] \[=\frac{(-6\hat{i}+6\hat{i}+\sqrt{2}\hat{k}).\,\left( \frac{{\hat{i}}}{2}+\frac{{\hat{j}}}{2}+\frac{{\hat{k}}}{\sqrt{2}} \right)}{\sqrt{\frac{1}{4}+\frac{1}{4}+\frac{1}{2}}}\] \[=\frac{-3+3+1}{\sqrt{\frac{4}{4}}}=1\]


You need to login to perform this action.
You will be redirected in 3 sec spinner