The train covered 60 km in 1 hour. Then he drove another 0.5 hour at a speed of 90 km / h.

The train covered 60 km in 1 hour. Then he drove another 0.5 hour at a speed of 90 km / h. With what average speed the train was moving.

To calculate the average speed of a given train, we apply the formula: Vav = S / t = (S1 + S2) / (t1 + t2) = (S1 + V2 * t2) / (t1 + t2), where S1 is the length of the first part of the path (S1 = 60 km); V2 – speed on the second part of the track (V2 = 90 km / h); t2 is the second elapsed time (t2 = 0.5 h); t1 is the first elapsed time (t1 = 1 hour).

Calculation: Vav = (60 + 90 * 0.5) / (1 + 0.5) = (60 + 45) / 1.5 = 105 / 1.5 = 70 km / h.

Answer: The average ground speed of a given train is 70 km / h.