CMC Medical CMC-Medical VELLORE Solved Paper-2011

  • question_answer
    The gravitational field in a region is given by\[I=\left( 4\widehat{i}+\widehat{j} \right)\]N/kg. The work done by this field is zero when a particle is moved along the line

    A) \[~x+y=6\]        

    B)  \[x+4y=6\]

    C)  \[y+4x=6\]       

    D)  \[x-y=6\]

    E)  \[x+y=8\]

    Correct Answer: C

    Solution :

                     Work done by the gravitational field is zero, when displacement is perpendicular to gravitational field. Here, gravitational field, \[I=4\,\hat{i}+\hat{j}\] If \[{{\theta }_{1}}\] is the angle which I makes with positive x-axis, then \[\tan {{\theta }_{1}}=\frac{1}{4}\] or            \[{{\theta }_{1}}={{\tan }^{-1}}\left( \frac{1}{4} \right)=14{}^\circ 6\] If \[{{\theta }_{2}}\] is the angle which the line\[y+4x=6\]makes with positive x-axis, then \[{{\theta }_{2}}={{\tan }^{-1}}(-4)=75{}^\circ 56\] So,          \[{{\theta }_{1}}+{{\theta }_{2}}=90{}^\circ \]ie, the line \[y+4x=6\]is perpendicular to I.


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