- #1

cheff3r

- 25

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## Homework Statement

Sally is a police officer who is standing in an intersection. A car driven by David approaches the intersection at a speed of 75 km/h. Sally blows her whistle (at a frequency of 900 hz) and signals the driver to stop. What does frequency does David hear? (speed of sound is 343 m/s). David does not stop and passes through the intersection and accelerates to 90 km/h, sally blows her whistle again, what frequency does David hear?

## Homework Equations

f'=(v-(v(D)-v(M)))/(v-(v(S)-v(M))*f

## The Attempt at a Solution

So the velocity of the median is zero, v is speed of sound =343 m/s , v(D) is David and at 75 km/h = 20.83 m/s and v(S) is sally = 0 and i also make it negative since traveling at sally

so i go

f'=(343-(-20.83))/343*900 = 954.65 Hz

next I do the same as above except i make the v(D) = 90 km/h = 25 and is positive

hence

f'=(343-25)/343*900 = 834.40Hz this is my problem shouldn't the traveling away Doppler affect give a greater frequency than started with?

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