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NEET Physics Work, Energy, Power & Collision / कार्य, ऊर्जा और शक्ति NEET PYQ-Work Energy Power and Collision

  • question_answer
    A body of mass 1 kg is thrown upwards with a velocity \[20\,m{{s}^{-1}}\]. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? \[(g=10\,m{{s}^{-1}})\] [AIPMT (S) 2009]

    A) 20 J

    B) 30 J                 

    C) 40 J

    D) 10 J

    Correct Answer: A

    Solution :

    Key Idea The energy lost due to air friction is equal to difference of initial kinetic energy and final potential energy.
    Initially body posses only kinetic energy and after attaining a height the kinetic energy is zero.
    Therefore, loss of energy \[=KE-PE\]
    \[=\frac{1}{2}\,m{{v}^{2}}-\,mgh\]
    \[=\frac{1}{2}\,\times 1\times 400-1\times 18\times 10\]
                \[=200-180=20\,J\]


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