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# Answer to Question #128787 in Mechanics | Relativity for Shilpa S

Question #128787
a train travels 50 km in half hour. it the stops at a station for 20 mins, before traveling for 2 hours at an average speed of 90 km/h what was the trains average speed over the whole journey
1
2020-08-14T16:01:35-0400

By definition, the average speed is:

"v_{av} = \\dfrac{l_{tot}}{T_{tot}}"

where "l_{tot}" is the total distance covered by the train in time "T_{tot}".

The distance covered during the first part of the journey is 50 km, during the second part is 0 km and during the third part "90km\/h\\cdot 2h = 180" km. Thus:

"l_{tot} = 50 km + 0km + 180km = 230km"

The time spent on the first part of the journey is 0.5h, on the second part "20\/60 = 1\/3 \\space h" and on the third part 2h, The total time is:

"T_{tot} = 0.5h + 1\/3\\space h + 2h = 17\/6 \\space h"

The average speed wil be:

"v_{av} = \\dfrac{l_{tot}}{T_{tot}} = \\dfrac{230km}{17\/6\\space h} \\approx 81.2 \\space km\/h"

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