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Mar11-10, 07:06 PM
P: 10
1. The problem statement, all variables and given/known data

A bus is moving at 37.00m/s towards a wall. The sound from the bus has an original wavelength of 0.1500m. The sound from the bus reflects off the wall. What frequency sound does an observer on the moving bus hear from the reflection??

2. Relevant equations

Moving Observer: fo = fs (1 + vo/v)
v = LaTeX Code: \\lambda f

3. The attempt at a solution

Is this doppler effect??

vo = 37.00m/s

Since v = LaTeX Code: \\lambda f

vi = LaTeX Code: \\lambda fi
f = v / LaTeX Code: \\lambda
= (343m/s)(0.1500) = 2286.667hz

Subbing into equation:

fo = (2286.667hz)(1 + 37m/s / 343m/s) = 2533hz

Ok, I ALSO tried another method...

Vs = 37 m/s

Therefore the speed of the wavefront is: vs + v
where v = 343m/s (speed of sound in air)

fs = 343m/s / 0.15m = 2286.667hz

Frequency observed is thus:

(v+vs/v-vs)fs = (343+37 / 343-37) (2286.667) = 2839.65hz

Both of these answers are choices in the multiple choice part, so this is becoming a frustrating question for me.

Help appreciated! Thanks!
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