Conceptual Questions:
1. Synchronized swimmers listen to their musical score underwater, in order to properly time their choreography. Does the support staff have to make any adjustment to the musical frequencies to account for the different speed of sound in water than in air?.
2. When a sound wave moves through a medium such as air, the motion of the molecules of the medium is in what direction (with respect to the motion of the sound wave)?
a. perpendicular
b. parallel
c. anti-parallel
d. Both choices B and C are valid.
3. What wave property of sound influences the perception of pitch?
4. What are the three qualities of perceived sound?
Numerical Problems: answers link to a help page.
1. A sound wave coming from a tuba has a wavelength of 1.5 m and travels to your ears at a speed of 345 m/s. What is the frequency of the sound you hear?
2. A series of ocean waves, 5.0 m between crests, moves past at 2 waves/s. Find their velocity.
3. Tripling the tension in a guitar string will change its natural frequency by what factor?
4. The lower A on a piano has a frequency of 27.5 Hz. If the tension in the 2-m long string is 304 N and one-half wavelength occupies the string, what is the mass of the string?
5. If a guitar string has a fundamental frequency of 500 Hz, what is the frequency of its second overtone?
6. You stand by the railroad tracks as a train passes by. You hear a 1000 Hz frequency sound when the train approaches, which then changes to 800 Hz as it goes away. How fast is the train moving?
7. I stretch a rubber band and "plunk" it to make it vibrate in its fundamental frequency. I then stretch it to twice its length and make it vibrate in the fundamental frequency once again. The rubber band is made so that doubling its length doubles the tension and reduces the mass per unit length by a factor of 2. The new frequency will be related to the old by a factor of:
8. How far away is a lightning strike if you hear the thunderclap 3 s after you see the lightning bolt strike? (v.sound = 340 m/s, v.light = 3 x108 m/s)
9. A bat, flying at 5 m/s toward a wall, emits a chirp at 50 kHz. If this sound pulse is reflected by the wall, what is the frequency of the echo received by the bat? (v.sound = 340 m/s)