BHU PMT BHU PMT Solved Paper-2001

  • question_answer
    Two items, each of 50 m length are moving parallel on parallel lines towards each other with speeds of\[10\,\,m/s\,\,and\,\,15\,\,m/{{s}^{2}}\]. The pass each other in.

    A)  \[6\,\,s\]                                            

    B)  \[2\,\,s\]

    C)  \[4\,\,s\]            

    D)  \[5\sqrt{\frac{2}{3}}\,\,s\]

    Correct Answer: C

    Solution :

    Key idea: Trains are moving towards each other, hence resultant speed is sum of two. The trains are moving in \[\xrightarrow[I=50\,m]{{{\text{v}}_{1}}{{=}_{10\,\text{m}/\text{s}}}}\] opposite directions. Relative speed \[{{v}_{1}}-\left( -{{v}_{2}} \right)\] \[=10+15=25\,\,m\xleftarrow[_{l=50m}^{{{v}_{2}}{{=}_{15m/s}}}]{}\] Relative distance              \[=50\,m+50\,m=100\,m\]          \[\xrightarrow[+ve]{}\] \[\therefore \text{Time}=\frac{\text{distance}}{\text{speed}}=\frac{100}{25}=4\,s\]                    


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