JEE Main & Advanced Sample Paper JEE Main Sample Paper-43

  • question_answer
    A machine which is 80% efficient, uses 20 J of energy in lifting up a 2 kg mass through a certain distance. The mass is then allowed to fall through that distance. The velocity at the end of its fall is

    A)  \[h\]                            

    B)  \[\frac{3}{4}h\]

    C)  \[\frac{1}{2}h\]                                 

    D)  \[\frac{1}{4}h\]

    Correct Answer: C

    Solution :

     We have, \[10-\frac{\lambda }{2}=(2n)\frac{\lambda }{2},\,\,n=0,\,\,1,\,2,...\] \[10=(2n+1)\frac{\lambda }{2},\,n=0,\,1,\,\,2,...\] Output energy = 16 J By conservation of energy, \[\Rightarrow \] \[\lambda =\frac{20}{2n+1},\,\,n=0,\,\,1,\,\,2,...\]

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