©1997 by Eric Mazur
Published by Pearson Prentice Hall
Upper Saddle River, NJ 07458
ISBN 0-13-565441-6
No portion of the file may be distributed, transmitted in any form, or included in other documents
without express written permission from the publisher.
Sound
The four figures below represent sound waves emitted by
moving source. Which picture(s) represent(s) a source
moving at less than the speed of sound?
Explanation
Three observers, A,B, and C are listening to a moving source
of sound. The diagram below shows the location of the
wavecrests of the moving source with respect to the three
observers. Which of the following is true?
1. The wavefronts move faster at A than at B and C.
2. The wavefronts move faster at C than at A and B.
3. The frequency of the sound is highest at A.
4. The frequency of the sound is highest at B.
5. The frequency of the sound is highest at C.
The following figure shows the wavefronts generated by an
airplane flying past an observer A at a speed greater than
that of sound. After the airplane has passed, the observer
reports hearing
1. a sonic boom only when the airplane breaks the sound
barrier, then nothing.
2. a succession of sonic booms.
3. a sonic boom, then silence.
4. first nothing, then a sonic boom, then the sound of
engines.
5. no sonic boom because the airplane flew faster than
sound all along.