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

  • question_answer
    If the resultant of the vectors \[3\widehat{i}+4\widehat{j}+5\widehat{k}\] and \[5\widehat{i}\text{ }+\text{ }3\widehat{j}\text{ }+\text{ }4\widehat{k}\] makes an angle \[\theta \] with x-axis, then \[cos\text{ }90{}^\circ \] is

    A) 0.07     

    B)        0.574

    C) 0.111   

    D)        0.123

    Correct Answer: B

    Solution :

    [b] The resultant vector\[=\left( 3\hat{i}+4\hat{j}+5\hat{k} \right)+\left( 5\hat{i}+3\hat{j}+4\hat{k} \right)=8\hat{i}+7\hat{j}+9\hat{k}\] \[\cos \theta =\frac{8}{\sqrt{{{8}^{2}}+{{7}^{2}}+{{9}^{2}}}}=0.574\]


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