BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    Two trains A and B of length \[\text{4}00\text{ m}\] each are moving on two parallel tracks with a uniform speed of \[\text{72 km}{{\text{h}}^{-1}}\] in the same direction, with A head of speed B. The driver of B decides to overtake A and accelerates by \[\text{1m}/{{\text{s}}^{\text{2}}}\]. if after\[\text{5}0\text{s}\], the guard of B just brushes past the driver of A, what was the original distance between them?

    A) \[\text{1}00\text{m}\]                 

    B) \[\text{115}0\text{m}\]

    C) \[\text{13}00\text{m}\]                               

    D) \[\text{125}0\text{m}\]

    Correct Answer: D

    Solution :

    Given that,\[{{u}_{A}}={{u}_{B}}=72km{{h}^{-1}}=72\times \frac{5}{18}=\text{20 m}{{\text{s}}^{\text{-1}}}\] Using the relations, \[s=ut+\frac{1}{2}a{{t}^{2}},\] we get \[{{s}_{B}}={{u}_{B}}t\frac{1}{2}a{{t}^{2}}=20\times 50+\frac{1}{2}\times 1\times {{(50)}^{2}}\] \[{{s}_{B}}=1000+1250=2250m\] Also, let \[{{s}_{A}}\] be the distance covered by the train A,  then \[{{s}_{A}}={{u}_{A}}\times t\] = 20 x 50 = 1000 m Original distance between the two trains \[={{s}_{B}}-{{s}_{A}}\] = 2250 -1000 = 1250 m


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