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NTSE Sample Paper NTSE SAT Practice Test-9

  • question_answer
    A body falls freely from rest. It covers as much distance in the last second of its motion as covered in the first three seconds. The body has fallen for a time of

    A) 3 s                               

    B) 5 s

    C) 7 s                               

    D) 9 s

    Correct Answer: B

    Solution :

    [b] \[{{S}_{nth}}=u+\frac{a}{2}(2n-1)\] \[=0+\frac{g}{2}(2n-1)\] \[=\frac{10}{2}(2n-1)\] \[=5(2n-1)\] Also. \[{{S}_{3}}=0+\frac{1}{2}g\times {{(3)}^{2}}\] \[=\frac{10}{2}\times 9=45\] As per question, \[{{S}_{nth}}={{S}_{3}}\] \[\therefore 5\text{ }\left( 2n-3 \right)=45\] or \[2n-1=9\] or n = 5 So, the body has fallen for a time of 5s.


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