CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    If\[\overrightarrow{u},\overrightarrow{v},\overrightarrow{w}\]be   vectors   such   that\[\overrightarrow{u}+\overrightarrow{v}+\overrightarrow{w}=\overrightarrow{0},\] and\[|\overrightarrow{u}|=3,|\overrightarrow{v}|=4,|\overrightarrow{w}|=5,\]then \[\overrightarrow{u}.\overrightarrow{v}+\overrightarrow{v}.\overrightarrow{w}+\overrightarrow{w}.\overrightarrow{u}\]equal to:

    A)  47                         

    B)         \[-47\]

    C)  0                                            

    D)  25

    E)  \[-25\]

    Correct Answer: E

    Solution :

    \[\because \] \[u+v+w=0\] \[\therefore \] \[|\overrightarrow{u}{{|}^{2}}+|\overrightarrow{v}{{|}^{2}}+|\overrightarrow{w}{{|}^{2}}+2(\overrightarrow{u}.\overrightarrow{v}+\overrightarrow{v}.\overrightarrow{w}\]\[+\overrightarrow{w}.\overrightarrow{u})=0\] \[\Rightarrow \]\[9+16+25+2(\overrightarrow{u}.\overrightarrow{v}+\overrightarrow{v}.\overrightarrow{w}+\overrightarrow{w}.\overrightarrow{u})=0\] \[\Rightarrow \]\[\overrightarrow{u}.\overrightarrow{v}+\overrightarrow{v}.\overrightarrow{w}+\overrightarrow{w}.\overrightarrow{u}=-25\]


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