# Car physics Sound Problem

1. Sep 22, 2005

### Eng67

I am having a problem with the following question.

A car is moving at 30 m/s. The cars horn is emmitting a 220 hz sound. The speed of sound is 343 m/s. How far does the the car move in one period of the sound emitted from the horn.

I am having a problem determining the distance formula.
The period of the 220 hz sound is 1/220hz = 4.54 ms

so in 4.54 ms the sound has travelled 1.55722 meters (343 * .00454)

Now the distance the car travels would be (4.54 ms * 30 m/s) = .1362 meters

2. Sep 22, 2005

### Andrew Mason

Yes. 1.557 meters is the wavelength of the sound: $\lambda = v/f$. The apparent wavelength depends on where the observer is. If the observer is behind the car, the wavelength appears to be 1.557+.1362. If the observer is in front, it is .1557 - .1362.

AM

3. Sep 22, 2005

### Eng67

Thanks!

I thought I was correct in my calculations.