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

  • question_answer
    A man throws bricks to a height of 12 m where they reach with a speed of 12 m/s. If he throws the bricks such that they just reach that height. What percentage of energy will he save?

    A) 19%                             

    B) 26%

    C) 38%                             

    D) 57%

    Correct Answer: C

    Solution :

    \[{{E}_{1}}=\frac{1}{2}mv_{2}^{2}+mgh=72\,\,m+12\,\,mg\] \[{{E}_{2}}=mgh=12\,mg\]             \[{{E}_{1}}-{{E}_{2}}=72\,mg\]             Percentage saving \[=\left( \frac{{{E}_{1}}-{{E}_{2}}}{{{E}_{1}}} \right)\times 100\]             \[=\frac{72\,m\times 9.81\times 100}{(72\,m+12\times 9.81\times m)}\]             = 38%


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