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

  • question_answer
    A man walks on a straight road from his home to market 2.5km away with a speed of 5 km/h. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km/h. The average speed of the man over the interval of time 0 to 40 min. is equal to -

    A) 5 km/h                        

    B) 25/4 km/h

    C) 30/4 km/h      

    D) 45/8 km/h

    Correct Answer: D

    Solution :

        A man walks from his home to market with a speed of 5km/h. Distance \[X=2.5km\]and \[time=\frac{d}{v}=\frac{2.5}{5}=\frac{1}{2}hr.\] And he returns back with speed of 7.5 km/h in rest of time of 10 minutes. Distance\[=7.5\times \frac{10}{60}=1.25km\] So, average speed\[=\frac{\text{Total distance}}{\text{Total time}}=\frac{(2.5\times 1.25)km}{(40/60)hr}=\frac{45}{8}km/hr.\]


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