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The “Doppler effect” refers to the universally perceived cha

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The “Doppler effect” refers to the universally perceived cha [#permalink] New post 16 Jul 2018, 01:25
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The “Doppler effect” refers to the universally perceived change in the apparent pitch of a sound when that sound is approaching or receding from the listener. Specifically, whenever the distance between the listener and the source of the sound is decreasing, the sound will be perceived by the listener as higher than its true pitch; whenever that distance is increasing, the sound will be perceived by the listener as lower than its true pitch. If the distance between the listener and the source is not changing, the listener will perceive the true pitch of the sound.

If the above principle holds, which of the following should be observed as an eastward-traveling train is approached by a westward-traveling train that is blowing its horn?

(A) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound lower than the true pitch.
(B) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound lower than the true pitch.
(C) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound higher than the true pitch.
(D) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound higher than the true pitch.
(E) Passengers in both trains should hear a sound that is higher than the true pitch.

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[Reveal] Spoiler: OA

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Re: The “Doppler effect” refers to the universally perceived cha [#permalink] New post 04 Sep 2018, 03:58
Hi Carcass,

Can you please explain how (D) is the answer for this question?

As per the question stem "an eastward-traveling train is approached by a westward-traveling train that is blowing its horn" is the case. However, as per the passage given, "whenever the distance between the listener and the source of the sound is decreasing, the sound will be perceived by the listener as higher than its true pitch".

In the case that is discussed, the distance between the trains is reducing. So, would'nt (E) Passengers in both trains should hear a sound that is higher than the true pitch. be the right answer?
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink] New post 04 Sep 2018, 09:13
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OFFICIAL EXPLANATION


Since the westbound train is blowing its horn, the westbound train is “the source of the sound.” Therefore, the passengers on the westbound train are traveling along with the source of the sound, and thus are neither approaching the source nor receding from it. Hence the westbound passengers should hear the true pitch of the sound.

According to the passage, the passengers in the eastbound train are approaching the source of the sound, the westbound train; the distance between the eastbound passengers and the sound is decreasing. Therefore, according to the given description of the Doppler effect, the eastbound passengers should perceive a sound that is higher than the true pitch.

(A) Passengers in the eastbound train do not hear the true pitch of the horn; passengers in the westbound train do.

(B) It is true that the westbound passengers hear the true pitch; the eastbound passengers, however, hear a sound that is higher than the true pitch.

(C) Passengers in the eastbound train do not hear the true pitch of the horn; passengers in the westbound train do.

(D) CORRECT. Westbound passengers do hear the true pitch of the sound. Eastbound passengers do hear a sound that is higher in pitch than the true sound.

(E) It is true that eastbound passengers hear a sound that is higher than the true pitch; the westbound passengers, however, hear the true pitch.


Actually, the passengers on the west traveling train are on it so they hear the true sound. The passengers on the east train hear a higher sound because the west train is approaching the east.

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Re: The “Doppler effect” refers to the universally perceived cha   [#permalink] 04 Sep 2018, 09:13
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