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An auto travels at the rate of 25 km/h for 4.0 minutes, then at 50 km/h for 8.0 minutes, and finally at 20 km/h for 2.0 minutes. Find (a) the total distance covered in km and (b) the average speed for the complete trip in m/s.

1 Answer

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(a) We use the formula,


Distance = speed * time

The total distance covered by auto,


= 25 \ km/h * ( 4.0 \ minutes * (1 \ h)/(60 \ minutes ) )  + 50 \ km/h * ( 8.0 \ minutes * (1 \ h)/(60 \ minutes )) + 20 \ km/h * ( 2.0 \ minutes * (1 \ h)/(60 \ minutes ) ) \\\\ = 9.1 \ km

(b)

Average speed = total distance / total time

Total time = 4/60 + 8 /60 + 2/60 = 14 /60

Thus, average speed


= (9.1)/((14)/(60) ) =39 \ km/ h

Average speed in m/s,


39 \ km/ h = (39 * 10^3 \ m)/(60 * 60 s) = 10. 83 \ m/s



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