Railways NTPC (Technical Ability) Engineering Mechanics and Strength of Materials Question Bank Engineering Mechanics

  • question_answer
    A cantilever beam of rectangular cross-section is subjected to a load W at its free end. If the depth of the beam is doubled and the load is halved, the deflection of the free end as compared to original deflection will be:

    A) Half                             

    B) One-eighth

    C) One-sixteenth    

    D) Double

    Correct Answer: A

    Solution :

    \[\delta =\frac{W{{L}^{3}}}{3EI}\] \[\delta \propto \frac{W}{I}\] \[{{\delta }_{1}}\propto \frac{12\,W}{b{{h}^{3}}}\] \[{{\delta }_{2}}\propto \frac{12\times \frac{W}{2}}{b\times {{(2h)}^{3}}}=\frac{6W}{8b{{h}^{3}}}=\frac{3}{4}=\frac{W}{b{{h}^{3}}}\] \[\frac{{{\delta }_{2}}}{{{\delta }_{1}}}=\frac{3}{4}\times \frac{1}{12}=\frac{1}{16}\]


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