What is the average speed of a train along the entire route if it first traveled 120 km at a speed

What is the average speed of a train along the entire route if it first traveled 120 km at a speed of 72 km / h, and then another 60 km at a speed of 54 km / h?

Given:

S1 = 120 kilometers = 120,000 meters – the first section of the route;

v1 = 72 km / h = 20 m / s – train speed on the first section of the track;

S2 = 60 kilometers = 60,000 meters – the second section of the route;

v2 = 54 km / h = 15 m / s – train speed on the second section of the track.

It is required to determine the average speed of the train along the entire track vav (m / s).

vav = S total / t total = (S1 + S2) / (S1 / v1 + S2 / v2) =

= (120,000 + 60,000) / (120,000 / 20 + 60,000 / 15) =

= 180,000 / (6000 + 4000) = 180,000 / 10000 = 18 m / s.

Answer: The average train speed is 18 meters per second.