1) The speed of sound is 343 m/s. A car’s horn produces a frequency of 400 Hz wh

Question

1) The speed of sound is 343 m/s. A car’s horn produces a frequency of 400 Hz when at rest. If the car is traveling West at 30 m/s toward an observer, what velocity must an observer have to hear a frequency of 400 Hz. (You must indicate both speed and direction. Indicate direction with words. Do not just use a sign.) 2) The index of refraction for air and water are 1.0 and 1.33 respectively. a) If light comes from air and hits at an incident angle of 70°, what is the angle of reflection? b) If light comes from air and hits at an incident angle of 70°, what is the angle of refraction? c) If light comes from water and hits at an incident angle of 70°, what is the angle of refraction?

Explanation / Answer

1.

Vs = speed of sound = 343 m/s

f = actual frequency = 400 Hz

V = speed of source of sound (car) = 30 m/s

f' = frequency observed

Using doppler's formula

f' = Vs f / (Vs - V)

f' = 343 (400) / (343 - 30) = 438.34 Hz

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