BHU PMT BHU PMT (Screening) Solved Paper-2005

  • question_answer
    What is the angle between\[\overrightarrow{A}=5\hat{i}-5\hat{j}\]and\[\overrightarrow{B}=5\hat{i}-5\hat{j}\]?

    A) \[90{}^\circ \]                                   

    B) \[45{}^\circ \]

    C)  Zero                                     

    D) \[60{}^\circ \]

    Correct Answer: C

    Solution :

     The scalar product of two vectors is defined as a scalar quantity equal to the product of their magnitude and cosine of the angle between them. \[\overrightarrow{A}.\overrightarrow{B}=|\overrightarrow{A}||\overrightarrow{B}|\cos \theta \] \[\Rightarrow \]\[\cos \theta =\frac{\overrightarrow{A}.\overrightarrow{B}}{|\overrightarrow{A}||\overrightarrow{B}|}=\frac{(5\hat{i}-5\hat{j}).(5\hat{i}-5\hat{j})}{\sqrt{{{5}^{2}}+{{5}^{2}}}\sqrt{{{5}^{2}}+{{5}^{2}}}}\]                                 \[=\frac{25+25}{25\times 2}=\frac{50}{50}=1\] \[\Rightarrow \]               \[\theta ={{0}^{o}}\] Alternative: As given,\[\overrightarrow{A}\]and\[\overrightarrow{B}\]are parallel vectors and hence, angle between parallel vectors is zero.


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