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
Messages
2
Reaction score
0

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.
 
Physics news on Phys.org
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
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Range of frequency heard by observer related to Doppler effect
Replies
8
Views
1K
Beats calculation/Doppler Effect
Replies
1
Views
2K
Calculating frequencies with the Doppler Effect
Replies
1
Views
3K
How do you calculate wind speed using the Doppler effect?
Replies
4
Views
3K
Doppler effect with 2 sound sources
Replies
3
Views
2K
Doppler effect and signs of the equation
Replies
3
Views
2K
Doppler effect and beat frequency
Replies
3
Views
2K
Blood flow velocity via Doppler effect
Replies
1
Views
2K
Spring and Microphone (Doppler Effect...?)
Replies
7
Views
3K
How can the Doppler effect be used as a motion detector?
Replies
16
Views
2K

Hot Threads

Recent Insights

Back
Top