Asked by Sher

A car horn is pitched at 520 Hz. The car travels along a straight road at a speed of 25 m/s. towards an observer walking at 2 m/. The speed of sound is 334 m/s. Calculate the frequency heard by the observer when:

(a) the car is moving towards the observer
Answered by Elena
http://en.wikipedia.org/wiki/Doppler_effect
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html
Answered by Sher
Can you give me the equation instead i'm still confused?
Answered by bobpursley
The equation is listed on both those sources, and you need to memorize it.
Answered by Sher
so which one is it? all of them are on both
Answered by Elena
I can’t understand the direction of Observer motion (towards or from the car?).
If the car and observer move towards each other,
their relative speed is 25-2 =23 m/s, then
f=f₀/[1-v/c)] =
=520/[1-23/334] = 558.5 Hz
If they move in the same direction v =25+2 = 27 m/s, then
f=f₀/[1-v/c)] =
=520/[1-27/334] = 565.7 Hz

If the car is moving FROM the observer
f=f₀/[1+ v/c)]
f= 520/[1+ 23/334)] =486.5 Hz
f=520/[1+ 27/334)] =481.1 Hz
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