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NEET NEET SOLVED PAPER 2017

  • question_answer
    Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time\[{{t}_{1}}.\]On other days, if she remains stationary on the moving escalator, then the escalator takes her up in time\[{{t}_{2}}.\]The time taken by her to walk up on the moving escalator will be           

    A) \[{{t}_{1}}-{{t}_{2}}\]                     

    B)  \[\frac{{{t}_{1}}+{{t}_{2}}}{2}\]

    C)  \[\frac{{{t}_{1}}{{t}_{2}}}{{{t}_{2}}-{{t}_{1}}}\]                  

    D) \[\frac{{{t}_{1}}{{t}_{2}}}{{{t}_{2}}+{{t}_{1}}}\]

    Correct Answer: D

    Solution :

                     Velocity of girl w.r.t. elevator\[=\frac{d}{{{t}_{1}}}={{v}_{ge}}\] Velocity of elevator w.r.t. ground\[{{v}_{eG}}=\frac{d}{{{t}_{2}}}\] then velocity of girl w.r.t. ground \[\vec{v}{{=}_{gG}}={{\vec{v}}_{ge}}+{{\vec{v}}_{eG}}\] i.e, \[{{v}_{gG}}={{v}_{ge}}+{{v}_{eG}}\] \[\frac{d}{t}=\frac{d}{{{t}_{1}}}+\frac{d}{{{t}_{2}}}\] \[\frac{1}{t}=\frac{1}{{{t}_{1}}}+\frac{1}{{{t}_{2}}}\] \[t=\frac{{{t}_{1}}{{t}_{2}}}{({{t}_{1}}+{{t}_{2}})}\]


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