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BHU PMT BHU PMT (Screening) Solved Paper-2007

  • question_answer
    A bread gives a boy of mass 40 kg an energy of 21 k-J. If the efficiency is 28%, then the height can be climbed by him using this energy, is

    A)  22.5m                                  

    B)  15m

    C)  10m                                     

    D)  5m

    Correct Answer: B

    Solution :

                     In order to climb a height h the boy utilizes potential energy\[=mgh\] In order to climb he will use the efficient energy. Also           \[1\,J={{10}^{3}}kJ\] Energy of one bread\[=21\,kJ=21\times {{10}^{3}}J\] Efficiency of boy   = 28% Hence, energy consumed by boy is                 \[=\frac{28}{100}\times 21000\] \[=5880J\]                                             ...(i) From law of conservation of energy, this energy is utilized in giving potential energy \[mgh\]where g is acceleration due to gravity. \[\therefore \] \[mgh=40\times 9.8\times h\]            ...(ii) Equating Eqs. (i) and (ii), we have \[40\times 9.8\times h=5880\] \[\Rightarrow \]               \[h=\frac{5880}{40\times 9.8}=15\,m\]


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