Question

Why is no sound heard by the observer when an object approaches him at a speed faster than that of sound?

a) The sound waves combine destructively.

b) The Doppler effect cancels out the sound.

c) The observer is moving away from the sound source.

d) The sound waves are absorbed by the object.

Answer 1

An observer hears no sound as an object exceeding the speed of sound approaches because the object overtakes its own sound waves, leading to a constructive interference known as a sonic boom behind it, only audible after the object passes.

Step-by-step explanation:

An observer cannot hear sound from an object approaching at a speed faster than that of sound because all the sound waves produced by the object are behind the source. When an object moves faster than the speed of sound, it means that it's overtaking the sound waves it produces.

As a result, the waves stack up and form a sonic boom behind the object. This sonic boom is effectively a constructive interference of sound, rather than destructive. This interference is only heard after the object has passed the observer, thus the observer hears no sound as the object approaches.