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Question

1. A monatomic ideal gas ( = 1.67) is contained within a box whose volume is 5.0 m3. The pressure of the gas is 7.00 105 Pa. The total mass of the gas is 2.5 kg. What is the speed of sound in the gas?

2. Suppose that sound is emitted uniformly in all directions by a public address system. The intensity at a location 26 m away from the sound source is 3.50 10-4 W/m2. What is the intensity at a spot that is 76 m away?

3.You are riding your bicycle directly away from a stationary source of sound and hear a frequency that is 2.5% lower than the emitted frequency. The speed of sound at the temperature that day is 350 m/s. What is your speed?

4.A 3.49 rad/s (33 1/3 rpm) record has a 3.00 kHz tone cut in the groove. If the groove is located 0.090 m from the center of the record (see drawing), what is the "wavelength" in the groove?

Answer 1

1. c = sqrt(1.67*7.00x10^5*5.0/2.5) = 1.53km/s.

2. We need to assume that the propergation of this sound wave is isotropic. Hence the requested intensity is:
(3.50x10^-4)*(26^2/76^2) = 4.1x10^-5 (W/m^2)

3. This is doppler effect. What is given is:
2.5% = v/350, hence v = 8.8 (m/s)

4. (3.49/s)*(0.090m)/(3.00x10^3/s) = 0.10 mm (answer)