A car approaches a stationary police car at 36 m/s. The frequency of the siren (relative to the police car) is 500 Hz. What is the frequency (in Hz) heard by an observer in the moving car as he approaches the police car? (Assume the velocity of sound in air is 343 m/s.)
a. 220
b. 448
c. 526
d. 552
e. 383
[Ques. 2] A point source emits sound waves with a power output of 100 watts. What is the sound level (in dB) at a distance of 10 m?
a. 139
b. 119
c. 129
d. 109
e. 10
[Ques. 3] A point source emits sound with a power output of 100 watts. What is the intensity (in W/m2) at a distance of 10.0 m from the source?
a. 7.96 102
b. 7.96 101
c. 7.96 100
d. 7.96 101
e. 7.96 103
[Ques. 4] By what factor is the intensity of sound at a rock concert louder than that of a whisper when the two intensity levels are 120 dB and 20 dB respectively?
a. 1012
b. 108
c. 106
d. 1010
e. 1011
[Ques. 5] By what factor will an intensity change when the corresponding sound level increases by 3 dB?
a. 3
b. 0.5
c. 2
d. 4
e. 0.3
[Ques. 6] A jet plane has a sound level of 150 dB. What is the intensity in W/m2?
a. 1
b. 100
c. 10
d. 1 000
e. 10 000
[Ques. 7] Calculate the intensity level in dB of a sound wave that has an intensity of 15 104 W/m2.
a. 20
b. 200
c. 92
d. 9
e. 10
[Ques. 8] Determine the intensity (in W/m2) of a harmonic longitudinal wave with a pressure amplitude of 8.0 103 N/m2 propagating down a tube filled with helium. ( = 0.179 kg/m3, v = 972 m/s.)
a. 3.7 107
b. 1.8 107
c. 9.2 108
d. 4.6 108
e. 1.5 109
[Ques. 9] The variation in the pressure of helium gas, measured from its equilibrium value, is given by P = 2.9 105 cos (6.20x 3 000t) where x and t have units m and s. Determine the speed (in m/s) of the wave.
a. 1 515
b. 153
c. 484
d. 828
e. 101
[Ques. 10] The variation in the pressure of helium gas, measured from its equilibrium value, is given by P = 2.9 105 cos (6.20x 3 000t) where x and t have units m and s, and P is measured in N/m2 . Determine the wavelength (in m) of the wave.
a. 1 500
b. 0.32
c. 477
d. 1.01
e. 0.50
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