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NEET Sample Paper NEET Sample Test Paper-68

  • question_answer
    Two trains one of length 100 m and another of length 125 m, are moving in mutually opposite directions along parallel lines, meet each other, each with speed 10 m/s. If their accelerations are \[0.3 m/{{s}^{2}}\,\,and\, 0.2 m/{{s}^{2}}\] respectively, then the time they take to pass each other will be

    A) 5 s                   

    B)   10 s

    C) 15 s                             

    D) 20 s

    Correct Answer: B

    Solution :

    Relative velocity of one train w.r.t. other \[= 10 + 10=20 m/s.\] Relative acceleration \[= 0.3 + 0.2= 0.5m/{{s}^{2}}\] If trains cross each other then from \[s=ut+\frac{1}{2}a{{t}^{2}}\] \[s={{s}_{1}}+{{s}_{2}}=100+125=225\] As, \[\Rightarrow \,\,\,225 =\,\,20\,t\,\,+\,\,\frac{1}{2}\times 0.5\times {{t}^{2}}\] \[\Rightarrow \,\,\,0.5{{t}^{2}}+40t\,-450=0\] \[\Rightarrow \,\,\,t=-\frac{40\pm \sqrt{1600+4.(005)\times 450}}{1}\,\,=\,\,-40\pm 50\] \[\therefore \,\,\,\,t= 10 sec \left( Taking +ve value \right)\]


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