IV-2 CW Sound 6. An officer walks at a velocity of 2 m/s directly toward a stude

Question

IV-2 CW Sound 6. An officer walks at a velocity of 2 m/s directly toward a student who is stationary and holding a radio playing loud music. Which of the following statements is true about this situation? I. The officer hears the music at a higher frequency than the student does Il. The officer hears the exact same frequency of sound that he would if he were standing still and the student were walking directly towards him at 2 m/s. Ill. The officer observes the sound waves from the radio to be moving at a lower velocity that the student does. A. I only B. Il only C. I and II only D. I, Il, and IlI 7. A driver travels northbound on a highway at a speed of 28.0 m/s. A police car, traveling southbound at a speed of 36.0 m/s, approaches with its siren producing sound at a frequency of 2450 Hz. (a) What frequency does the driver observe as the police car approaches? (b) What frequency does the driver detect after the police car passes him?

Explanation / Answer

7. from the given data

driver travels northwards, v = 28 m/s

police car travelling south bpound, u = 36 m/s

frequency of siren, f = 2450 Hz

a. when the car is approaching

from doppler's effect

f = (c + v)fo/(c - u)

for air, c = 334 m/s

hence

f = (334 + 28)*2450/(334 - 28) = 2898.36601307 Hz

b. when the car is moving away

from doppler's effect

f = (c - v)fo/(c + v)

f = 2070.9944751381 Hz

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