What Speed is the Racecar Moving?

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SUMMARY

The discussion centers on calculating the speed of a racecar based on the Doppler effect, specifically how the pitch of the sound drops by a musical interval of a fourth, indicating that the frequency after passing is 0.75 times the original frequency. The correct speed of the racecar is determined to be 68 m/s, as derived from the relationship between frequency change and velocity. Participants are encouraged to apply the Doppler effect formula to solve similar problems effectively.

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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?

a. 68 m/s
b. 49 m/s
c. 61 m/s
d. 72 m/s
 
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I cannot figure out how to work this problem out, any help would be great. Thanks in advance.
 
Think of what formulae that comes to your mind when you do this question.
 

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