week-6-discussion

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Physics

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Apr 3, 2024

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Physics 5B - Week 6 Discussion Name: UID: Emergency vehicles need to strike a careful balance between drawing attention with sound sirens and protecting the public (as well as EMTs) against hearing loss. According to the CDC, ±loud noise above 120 dB can cause immediate harm to your ears.² However, an Illinois regulation requires that all ambulance sirens be su³ciently loud to produce a sound intensity level of 100 dB at 50 ft away from the vehicle. 1. The sound wave from an ambulance can’t propagate evenly in all directions because it gets re´ected upward by the road. Instead, assume that the sound wave propagates evenly in all directions above horizontal, making a hemispherical wavefront. Find a function for the area of this wavefront A ( r ) in terms of the radius r . 2. Convert the sound intensity level 100 dB into a sound intensity in W / m 2 . 3. Assume that the sound intensity level is 100 dB at 50 feet away from the ambulance. Using the area function from 1. and your answer to 2. , calculate the power of the siren speaker in Watts. Note that one meter is about 3.28 feet. 1
4. How close can you stand (in feet) to a stationary ambulance with its siren on before sustaining immediate hearing damage? 5. While you are standing on the sidewalk, an ambulance travels by at 40 mph. As it passes by, you notice the pitch of the siren change. Does the frequency increase or decrease? Calculate the ratio between the observed frequency when the ambulance is moving towards you and the observed frequency when the ambulance is moving away from you. Take the speed of sound in air at STP to be 343 m / s. 2
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