# Determine the length of a train traveling at a speed of 40 km / h, sees within 3 seconds

Determine the length of a train traveling at a speed of 40 km / h, sees within 3 seconds an oncoming train 75 m long. At what speed is the oncoming train moving?

Initial data: V1 (speed of the first train) = 40 km / h; t (time of visibility of the oncoming train) = 3 s; S (length of the oncoming train) = 75 m.

1) Determine the speed of the oncoming traffic of two trains: V = V1 + V2 = S / t = 75/3 = 25 m / s (in km / h, this speed is 90 km / h).

2) Let’s calculate the speed of the oncoming train: V2 = V – V1 = 90 – 40 = 50 km / h.

Answer: The oncoming train will move at a speed of 50 km / h.

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