Question

You are standing at x = 0 m, listening to a sound that is emitted at frequency $f_0$. The graph of FIGURE Q16.12 shows the frequency you hear during a 4-second interval. Which of the following describes the sound source? Explain your choice.

A. It moves from left to right and passes you at t = 2 s.

B. It moves from right to left and passes you at t = 2 s.

C. It moves toward you but doesn’t reach you. It then reverses direction at t = 2 s.

D. It moves away from you until t = 2 s. It then reverses direction and moves toward you but doesn’t reach you

Short answer

Option (D) is correct.

Step-by-step solution

Step 1. Write the given information.

The frequency of the sound source is f_o

The change in frequency of the sound with respect to time is given in the graph.

Step 2. To analyze the graph

• The dotted line in the graph shows the original frequency of the sound source.
• In the first 2 seconds, the frequency heard is less than the original frequency
• After 2 seconds, the frequency heard is more than the original.
• The sound source is moving away from the listener which is why the frequency heard is less than the original. After time t = 2sec, the source comes towards the listener, hence, the frequency heard is higher than the original frequency. Thus, the source moves away from the listener till the time 2 sec and then reverses the direction to move toward the listener but it does not reach the listener.

Therefore, option D is correct.