# physics

A train moving with a speed of 31.8 m/s sounds a 136-Hz 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

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1. 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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bobpursley

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