2) A person is riding her bike on a road running parallel to railroad tracks, Tr
ID: 2042540 • Letter: 2
Question
2) A person is riding her bike on a road running parallel to railroad tracks, Train A, traveling in the same direction as the bike rider, sounds a 400 Hz train whistle as it approaches and passes the bike rider. Train B is traveling in the opposite direction as the bike rider as it also emits a train whistle of 400 Hz as it it approaches and passes the bike rider. In which of the following situations will the bike rider hear the highest and lowest frequency?a) A approaches, A moves away
b) B approaches, A moves away
c) A approaches, B moves away
d) B approaches, B moves away
e) More information is needed
Answer/Explanation (Why?)
Explanation / Answer
In classical physics, where the speeds of source and the receiver relative to the medium are lower than the velocity of waves in the medium, the relationship between observed frequency f and emitted frequency f0 is given by
f = (c +vr/ c + vs)fo
where
c is the velocity of waves in the medium
vr is the velocity of the receiver relative to the medium; positive if the receiver is moving towards the source.
vs is the velocity of the source relative to the medium; positive if the source is moving away from the receiver.
we get maximum at a is source moving towards and B is moving towards train
implies highest when B approache s minimum when A moves away
answer is B b) B approaches, A moves away
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