Average speed

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Average speed is the ratio of total distance and the total time taken to complete that distance.

          Average speed = Total distance covered/total time

The unit of average speed is same as speed or velocity that is m/s.

If S1, S2 and S3 distance covered in t1, t2 and t3 time respectively, then

                   Average speed = (S1 + S2 + S3)/(t1 + t2 + t3)
 

Example: A car travels a distance of 60 miles for 4 hrs and 90 miles for next 6 hrs. Calculate its average speed.

Solution: Given that,
          Total distance = 60 miles + 90 miles = 150 miles
          Total time = 4 hr + 6 hr = 10 hr
Average speed = Total distance/total time
                   = 150/10 = 15 miles per hour

 
Example: A car travels at an average speed of 156.8 km/h for 2.00 h and then at an average speed of 82.2 km/h during a second hour. What is the car's average speed during the 4.00 h interval?

Solution: Given that,
          First distance = speed x time = 156.8 x 2 = 313.6 km
          Second distance         = 82.2 x 2 = 164.4 km
Total distance = 313.6 + 164.4 = 478 Km
Total time = 4 hr
          Average speed = total distance/total time
                             = 478/4 = 119.5 Km/h
In other method we can calculate the average of the two average speed.
                   Average speed = (156.8 + 82.2)/2 = 119.5 Km/h
         
 

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