Question

3. Violating the six feet rule, a screaming youth skateboards toward a stationary physics student. The source frequency of the youth's scream is 750.0Hz, as shown below. The Doppler shift (Af=f'-f.) for the observed sound frequency is +15.0Hz, Treat sound waves as spherical and assume the speed of sound, V sound, is 343.0 m/s at this location. (1 pt each) i. How fast is the skateboarder moving toward the observer? Student Fearless Youth (observer) (source) ii. As the skateboarder passes by the student, he accelerates to a final speed of 10.0m/s. At this new speed, determine the sound frequency heard by the student as the youth skateboards away at 10.0m/s. Fearless Youth Student (source) (observer)

Answer 1

3) Let f': frequency heared by student fos Actual frequency of sound soune = 750 Hz Af - f'- to + 15.0 H2 : f'- Af + fo 15.0+ 750 = 765 HZ V = speed of sound - 343.0 m/s V. speed of observer (student) Vs speed of source speed of skateboarder 0 m/s an 1) when source g Observer moving towards each other in that case the change frequency heared is V + Vo V - Vs But here observed is at rest, so Vo=0 m/s f' = to cl f' fo V U-Vs fo V to v f'( V- Vs) f'v - f' Vs fv-for į Vs (f'-t.) v f' :. Vs

(765-750) 343 : Us 6.73 m/s 765 Vs = 6.73 m/s At this speed skateboarder is moving towards the Observer. 2) now Vs = speed of skateboardes 10.0 m/s f'= } In this case, soune is moving away from the observer so formula used here is V-Vo fo V + Vs vtvs Here, also, Vo = Stedent (obsesver) is at rest = Omis 343 = 750 x 343 + 10 f f'a 728.8 Hz