physics
posted by cassie .
A train moving with a speed of 31.8 m/s sounds a 136Hz horn. Suppose a stationary observer sounds a horn that is identical to the one on the train. What frequency is heard from this horn by a passenger in the train.
a) 9.8 Hz
b) 31.8 Hz
c) 99 Hz
d) 115 Hz
e) 149 Hz
The fundamental of a closed organ pipe is 261.6 Hz (middle C). The second harmonic of an open organ pipe has the same frequency
what are the lengths of the closed pipe?
A)1m b) .54m C).48 m d) .33m
What are the lengths of open pipe?
A)1.31m b)1m c).37m d).24m

physics 
bobpursley
First question: It depends on the relative speed the passenger has...is he going away, or coming toward the sound?
On the second question, the length of the pipe if closed on one end, is lambda/4, or length= 1/4 340/261= you do it.
The second harmonic has a length lambda, so l= 340/261= you do it.
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