At an air show, Julia saw a fighter jet fly by. Three seconds later she heard the sonic boom of the sound barrier being broken. Did the jet break the sound barrier as it passed Julia? Explain your answer.

Answer:

No, the jet did not break the sound barrier at Julia’s location. It broke the sound barrier before it reached her. Because the speed of light is significantly faster than the speed of sound, Julia saw the jet pass by first. The three-second delay before hearing the sonic boom indicates that the jet was already traveling at supersonic speeds and that the sound waves it generated took longer to reach her ears than the light reflecting off the jet.