a) lower because the sound-wave fronts reach the platform at a frequency lower than the frequency at which they are produced
explanation :3
If the train is <u>leaving</u> the train station, then the people who are standing on the platform would hear a sound with a lower frequency since the train is moving further away. ^^
El kilogramo de fuerza, o kilopond, es una unidad de fuerza métrica gravitacional. Es igual a la magnitud de la fuerza ejercida sobre un kilogramo de masa en un campo gravitatorio de 9.80665 m / s².
