(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

The pitch of the sound from a racecar engine drops the musical interval of a fourth when it passes the spectators. This means the frequency of the sound after passing is 0.75 times what it was before. How fast is the racecar moving?

1. 61 m/s

2. 49 m/s

3. 72 m/s

4. 68 m/s

2. Relevant equations

fo = fs / 1 - (vs/v)

3. The attempt at a solution

I tried using 75 = 100 / (1 - (vs/331) to solve for the speed of the source, but my answer was way off...there's got to be something i'm missing. am i correct in thinking i need to use v = 331 for the speed of sound? then what do i use for fo and fs?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Doppler Effect of race car

**Physics Forums | Science Articles, Homework Help, Discussion**