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7th Class Science Time and Motion Question Bank Motion and Time

  • question_answer
    A train travels 40 km at a uniform speed of 30 km\[{{\text{h}}^{-\text{1}}}\]. Its average speed after traveling another 40 km is 45 km \[{{\text{h}}^{-\text{1}}}\] for the whole journey. Its speed in the second half of the journey is

    A) 45kmh \[{{\text{h}}^{-\text{1}}}\]             

    B) 90kmh \[{{\text{h}}^{-\text{1}}}\]

    C) 60kmh \[{{\text{h}}^{-\text{1}}}\]             

    D) None of these

    Correct Answer: B

    Solution :

        Let speed of the train in later half \[=x\], then the time taken to travel later \[40km=40/x\]hours Total time taken\[=40/30+40/x\] Average speed\[=\frac{80}{4/3+40x}=45\] Solve the equation to find value of x


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