JEE Main & Advanced Physics Vectors Question Bank Multiplication of Vectors

  • question_answer
     If for two vector \[\overrightarrow{A}\] and \[\overrightarrow{B}\], sum \[(\overrightarrow{A}+\overrightarrow{B})\] is perpendicular to the difference \[(\overrightarrow{A}-\overrightarrow{B})\]. The ratio of their magnitude is

    A)                 1             

    B)                 2

    C)                 3             

    D)                 None of these

    Correct Answer: A

    Solution :

                        \[(\overrightarrow{A}+\overrightarrow{B})\] is perpendicular to \[(\overrightarrow{A}-\overrightarrow{B})\]. Thus                 \[(\overrightarrow{A}+\overrightarrow{B})\].\[(\overrightarrow{A}-\overrightarrow{B})\] = 0                 or \[{{A}^{2}}+\overrightarrow{B}\,.\,\overrightarrow{A}-\overrightarrow{A}\,.\,\overrightarrow{B}-{{B}^{2}}=0\,\]                 Because of commutative property of dot product  \[\overrightarrow{A}.\overrightarrow{B}=\overrightarrow{B}.\overrightarrow{A}\]                 \[\therefore \]\[{{A}^{2}}-{{B}^{2}}=0\] or \[A=B\]                 Thus the ratio of magnitudes A/B = 1


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