Situation 15.1
A train is approaching a signal tower at a speed of 40 m/s.The train engineer sounds the 1000 Hz whistle and a switchman in the tower responds by sounding the 1200 Hz siren.The air is still and the speed of sound is 340 m/s.
-In Situation 15.1,the frequency of the tower siren tone,heard by the engineer,in SI units,is closest to:

Question

Quizplus · Accepted Answer

The frequency heard by the engineer is affected by the Doppler effect. Since the train is moving towards the source of the sound (the siren), the frequency increases. The formula for the observed frequency is f' = f * (v + vo) / (v - vs), where f is the source frequency, v is the speed of sound, vo is the observer's speed, and vs is the source's speed. Here, the observer (engineer) is moving towards the source, so vo = 40 m/s, vs = 0, and f = 1200 Hz. Thus, f' = 1200 * (340 + 40) / 340 = 380/340 * 1200.

Situation 15.1 A Train Is Approaching a Signal Tower at a Speed