Posted by **Sher** on Thursday, July 25, 2013 at 4:07pm.

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

- Physics Help ASAP -
**Elena**, Thursday, July 25, 2013 at 4:44pm
http://en.wikipedia.org/wiki/Doppler_effect

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html

- Physics Help ASAP -
**Sher**, Thursday, July 25, 2013 at 4:51pm
Can you give me the equation instead i'm still confused?

- Physics Help ASAP -
**bobpursley**, Thursday, July 25, 2013 at 4:53pm
The equation is listed on both those sources, and you need to memorize it.

- Physics Help ASAP -
**Sher**, Thursday, July 25, 2013 at 5:20pm
so which one is it? all of them are on both

- Physics Help ASAP -
**Elena**, Thursday, July 25, 2013 at 5:34pm
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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