What is the Speed of the Car Based on the Doppler Effect of Sound?

AI Thread Summary
The discussion revolves around calculating the speed of a car using the Doppler Effect, where a policeman observes a 10% decrease in the pitch of the car's horn as it passes by. The relevant formula is f2 = f1 [v - v(listener)]/[v - v(source)], with the velocity of sound given as 330 m/s. The confusion arises regarding the car's motion relative to the policeman, as it approaches and then moves away. Clarification is provided that the car's speed is the same in both directions. The conversation emphasizes understanding the Doppler Effect in this context to solve the problem accurately.
Kinar
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Homework Statement


A policeman detects a drop of 10% in the pitch of the horn of a motor car as it crosses him. If the velocity of sound is 330ms^-1, calculate the speed of the car.


Homework Equations


f2 = f1 [v - v(listener)]/[v - v(source)]
where f2 = apparent frequency
f1 = true frequency


The Attempt at a Solution


I'm confused about how the car crosses him. Please help.
 
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Kinar said:

Homework Statement


A policeman detects a drop of 10% in the pitch of the horn of a motor car as it crosses him. If the velocity of sound is 330ms^-1, calculate the speed of the car.


Homework Equations


f2 = f1 [v - v(listener)]/[v - v(source)]
where f2 = apparent frequency
f1 = true frequency


The Attempt at a Solution


I'm confused about how the car crosses him. Please help.
Welcome to Physics Forums.

At first, the car is moving toward the policeman at speed vsource. It passes by the policeman, and is then moving away from him at the same speed.
 
thanks
 
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