Chapter 16 part 2 (sound waves) Homework
1) A hammer strikes one end of a thick iron rail of length 8.50 m. A microphone located at the opposite
end of the rail detects two pulses of sound, one that travels through the air and a longitudinal wave that
travels through the rail. a) Which pulse reaches the microphone first? b) Find the separation in time
between the arrivals of the two pulses.
2) The intensity of a sound wave at a fixed distance from a speaker vibrating at a frequency f is I.
a) Determine the intensity that results if the frequency is increased to f' while a constant displacement
amplitude is maintained. b) Calculate the intensity if the frequency is reduced to f/2 and the
displacement amplitude is doubled.
3) A firework charge is detonated many meters above
the ground. At a distance d1 = 500 m from the explosion,
the acoustic pressure reaches a maximum of ΔPmax =
10.0 Pa. Assume the speed of sound is constant at 343
m/s throughout the atmosphere over the region considered, the ground absorbs all the sound falling on
it, and the air absorbs sound energy as described by the rate 7.00 dB/km. What is the sound level (in
decibels) at a distance of d2 = 4.00E3 m from the explosion?
4) A tuning fork vibrating at 512 Hz falls from rest and accelerates at 9.80 m/s2. How far below the
point of release is the tuning fork when waves of frequency 485 Hz reach the release point? (Don't
forget that sound takes time to propagate!)
5) Standing at a crosswalk, you hear a frequency of 560 Hz from the siren of an approaching
ambulance. After the ambulance passes, the observed frequency of the siren in 480 Hz. Determine the
ambulance's speed.
6) Two ships move along a line due east. The trailing
vessel has a speed relative to a land-based observation
point of v1 = 64.0 km/h and the leading ship has a speed
of v2 = 45.0 km/h relative to that point. The two ships
are in a region of the ocean where the current is moving uniformly due west at vcurrent = 10.0 km/h. The
trailing ship transmits a sonar signal at a frequency of 1200.0 Hz through the water. What frequency is
monitored by the leading ship?
7) A bat is flitting about in a cave, navigating via ultrasonic bleeps. Assume that the sound emission
frequency of the bat is 39,000 Hz. During one fast swoop directly toward a flat wall surface, the bat is
moving at 1/40 of the speed of sound in air. What frequency does the bat hear reflected off the wall?
8) Two trains are headed towards each other at a speed of 30. m/s relative to the ground. One train is
blowing a whistle at 500. Hz. a) What frequency will be heard on the other train in still air? b) What
frequency will be heard on the other train if the wind is blowing at 30. m/s toward the whistle and away
from the listener? c) What frequency will be heard if the wind direction is reversed?
9) A line source of sound (for instance, a long, noisy freight train on a straight track) emits a cylindrical
expanding sound wave. Assuming that the air absorbs no energy, find how a) the sound intensity I and
b) the amplitude sm of the wave depend on the perpendicular distance r from the source.
1) a: iron, b: 0.0234 s
2) a: I ' =I f ' 2 / f 2 , b: I' = I
3) 68.3 dB
4) -19.7 m
5) 26.4 m/s
6) 1204.2 Hz
7) 41 kHz
8) a: 596 Hz, b: 606 Hz, c: not given
9) a: not given, b: not given