Question

You are standing on a bridge above the railroad tracks of the French High Speed Train (TGV). The train is approaching you with a constant speed of 81.0 m/s. (81.0 m/s = 291.6 km/h = 182.0 mi/h.) The train gives a 7.20 s long horn signal. How long does the signal last for you? The train reaches you only after it is finished emitting the horn signal. For the speed of sound use 334.0 m/s.

Answer 1

The time it takes for the sound to travel from the train to the observer on the bridge is given by:

distance = speed × time

The distance is the same as the distance the train travels during the duration of the horn signal, which is:

distance = speed × time = 81.0 m/s × 7.20 s = 583.2 m

The time it takes for the sound to travel this distance is:

time = distance / speed of sound = 583.2 m / 334.0 m/s = 1.744 s

Therefore, the horn signal lasts for 1.744 seconds for the observer on the bridge.