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JEE Main & Advanced Physics Two Dimensional Motion Question Bank Self Evaluation Test - Motion in a Plane

  • question_answer
    If \[A=5\widehat{i}+7\widehat{j}-3\widehat{k}\] and \[B=2\widehat{i}+2\widehat{j}-a\widehat{k}\] are perpendicular vectors, the value of a is:

    A) \[-\,2\]  

    B)        8   

    C) \[-\,7\]              

    D)        \[-\,8\]

    Correct Answer: D

    Solution :

    [d] \[\text{\vec{A}}\,\text{.}\,\text{\vec{B}}\,\text{=}\,\text{0}\] \[\text{or }\left( 5\hat{i}+7\hat{j}-3\hat{k} \right).\left( 2\hat{i}+2\hat{j}-a\hat{k} \right)=0\] \[\therefore 5\times 2+7\times 2+3a=0\text{ }or\text{ }a=-8\]


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