While you are sounding a tone on a toy whistle, you notice a friend running toward you. If you want her to hear the same frequency that you hear even though she is approaching, you must
A) stay put.
B) run towards her at the same speed.
C) run away from her at the same speed.
D) stay put and play a note of higher frequency.
E) run towards her and play a note of higher frequency.

Question

Quizplus · Accepted Answer

Due to the Doppler effect, as your friend approaches, she would hear a higher frequency than you are actually playing. To compensate for this and make her hear the same frequency you do, you would need to move away from her at the same speed, which would lower the frequency she hears, counteracting the effect of her approach.

While You Are Sounding a Tone on a Toy Whistle