KVPY Sample Paper KVPY Stream-SX Model Paper-30

  • question_answer
    The vectors \[\overrightarrow{a}=-4\hat{i}+3\hat{k},\,\,\overrightarrow{b}=14\hat{i}+2\hat{j}-5\hat{k}\] are co-initial. The vector \[\overrightarrow{d}\] which is bisecting the angle between the vectors \[\overrightarrow{a}\] and \[\overrightarrow{b}\] and is having the magnitude \[\sqrt{6}\], is

    A) \[\hat{i}+\hat{j}+2\hat{k}\]

    B) \[\hat{i}-\hat{j}+2\hat{k}\]

    C) \[\hat{i}+\hat{j}-2\hat{k}\]

    D) none

    Correct Answer: A

    Solution :

    A vector along the angle bisector = \[\hat{a}+\hat{b}\]
    \[=\frac{(-4\hat{i}+3\hat{k})}{5}+\frac{(14\hat{i}+2\hat{j}-5\hat{k})}{15}\]
    \[\frac{-12\hat{i}+9\hat{k}+14\hat{i}+2\hat{j}-5\hat{k}}{15}\]
    \[=\frac{2(\hat{i}+\hat{j}+2\hat{k})}{15},\vec{d}=\sqrt{6}\left( \frac{\left( \hat{i}+\hat{j}+2\hat{k} \right)}{\sqrt{{{1}^{2}}+{{1}^{2}}+{{2}^{2}}}} \right)\]\[\therefore \,\,\,\,\,\,\,\vec{d}=\hat{i}+\hat{j}+2\hat{k}\]


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