Which of the following describes the sound source? Which of the following describes the sound source? It moves from left to right and passes you at t = 2 s. It moves from right to left and passes you at t = 2 s. It moves toward you but doesn't reach you. It then reverses direction at t = 2 s. It moves away from you until t = 2 s. It then reverses direction and moves toward you but doesn't reach you.

Complete Question:

You stand at x = 0 m, listening to a sound that is emitted at frequency f0. The figure shows the frequency you hear during a four-second interval.  

Which of the following describes the motion of the sound source?  

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

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

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

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

Correct

Option D. It moves away from you until t = 2s and then reverses direction and moves towards you but doesn't reach you.

Explanation:

As the sound is heard by the observer at a time interval of 4s, this means as per the figure, the sound is moving away from the observer. This is because, the frequency is decreasing with increase in time in the figure.

Due to Doppler shift, if the source is moving away from the observer than there will be decrease in the frequency heard by the observer. Then there is an increase in the frequency, that means the direction of the source is reversed and it is moving towards the observer that is you.

But since, the frequency is not matching with the source frequency, it means it has not reached the observer. Thus, the last option describes the sound source. As it says that the source is first moving away from the observer till 2s and then it reverses direction and moves towards the observer but it did not reach it.

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