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JCECE Engineering JCECE Engineering Solved Paper-2004

  • question_answer
    The resultant of two forces \[P\] and \[Q\] is \[R\]. If the direction of \[P\] is reversed keeping the direction \[Q\] same, the resultant remains unaltered. The angle between \[P\] and \[Q\] is:

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

    B) \[{{60}^{o}}\]

    C) \[{{45}^{o}}\]                                    

    D) \[{{30}^{o}}\]

    Correct Answer: A

    Solution :

    According to the given condition                 \[{{R}^{2}}={{P}^{2}}+{{Q}^{2}}+2PQ\cos \alpha \] and        \[{{R}^{2}}={{P}^{2}}+{{Q}^{2}}-2PQ\cos \alpha \] \[\Rightarrow \]               \[{{P}^{2}}+{{Q}^{2}}+2PQ\cos \alpha \] \[\Rightarrow \]               \[4PQ\cos \alpha =0\] \[\Rightarrow \]               \[\alpha ={{90}^{o}}\]


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