a) When at rest, two trains have sirens that emit a frequency of 300 Hz. The tra

Question

a) When at rest, two trains have sirens that emit a frequency of 300 Hz. The trains travel toward one another and toward an observer stationed between them. One of the trains moves at 26.5 m/s, and the observer hears a beat frequency of 2.8 beats per second. What is the speed of the second train, which travels faster than 26.5 m/s?

m/s

b)A sound wave from a siren has an intensity of 113.6 W/m2 at a certain point, and a second sound wave from a nearby ambulance has an intensity level 8 dB greater than the siren's sound wave at the same point. What is the intensity level of the sound wave due to the ambulance?

Explanation / Answer

f' = f v/(v-vs) = 300 * 343.2 / (343.2 - 26.5) = 325.1 hz

f'' = f v/(v-vs) = 300 * 343.2 / (343.2 - v)

f'' - f' = 2.8

f'' = 2.8 + 325.1 = 327.9

327.9 = f v/(v-vs) = 300 * 343.2 / (343.2 - v)

v = 29.2 m/s

b)

113.6 W/m^2

10 log10 (113.6/1x10^-12)

=140.55 db

ambulance intensity

8 + 140.55 = 148.55 db

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