# Passenger trains run on parallel tracks towards each other, the length of each train is 150 m.

Passenger trains run on parallel tracks towards each other, the length of each train is 150 m. The speed of the first is 90 km / h. The passenger on the first train noticed that the oncoming train passed him in 2 seconds. Determine the speed of the oncoming train.

Data: oncoming traffic; L (length of each train) = 150 m; V1 (speed of the first train) = 90 km / h (in SI V1 = 25 m / s); t (duration of observation by a passenger of an oncoming train) = 2 s.

To determine the required speed of the oncoming train, we use the equality: V1.2 = V1 + V2 = L / t, whence V2 = L / t – V1.

Calculation: V2 = 150/2 – 25 = 75 – 25 = 50 m / s or 180 km / h.

Answer: The sought speed of the oncoming train is 180 km / h (50 m / s).

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