Solved Examples on Average Speed

A train travels at a speed of  300 km/hr for 2 hours and then slows down to 220 km/hr for the next 2 hours. What is the average speed of the train?

Solution: Distance covered in the first 2 hours, D1 = 300 * 2 = 600 miles

Distance covered in the next 2 hours, D2 = 220 * 2 = 440 miles

Total distance covered, D= D1 + D2

D = 600 + 440 = 1040 miles

Total time taken = 4 hours

Thus, the average speed of the train =

Total Distance travelled (D)Total Time taken (T)Total Distance travelled (D)Total Time taken (T)

= 1040/4 = 260 m/s

2. A particle moves with a speed of 4m/s for 20s. It again moves with a speed of 6m/s for another 20s and finally moves with a speed of 8m/s for next 20s. Calculate the average speed of the particle? (in m/s)

Solution: Distance= speed x time

Distance travelled in first 20s, D1 = 20s × 4 m

= 80 m

Distance travelled in next 20s, D2 = 20 × 6 m

= 120 m

Distance travelled in the last 20s, D3 = 20 × 8 m

=100 m

Total distance travelled by particle, D = 80 + 120 + 160 m

= 360 ms

Total time taken, T = 20×3 = 60s

Therefore, the average speed, S = D/T

= 360/60 m/s

= 60 m/s

3. A person goes from Point A to Point B in 10s and returns back in 8s. If the distance between A and B is 36m, find the average speed of the person.

Solution: Here total distance covered = 72m

Total time taken = 18s

Therefore, average speed  =

Total distance coveredTotal time taken=7218Total distance coveredTotal time taken=7218 = 4 m/s.