# physic

A source of sound emits waves at a frequency 650 Hz. An observer is located at a distance 190 m from the source. Use m/s for the speed of sound.

(a) Assume completely still air. How many wavefronts (full waves) are there between the source and the observer?

(b) If the observer is moving away from the source at a (radial) velocity m/s, how does the number of wavefronts found in part (a) change with time? For the answer, give the rate of change of , namely (in Hz)

(c) By comparing the difference of the rate of wavefronts leaving and wavefronts entering the region between source and observer, calculate the frequency observed by the moving observer. (in Hz)

hint: how does the difference relate to the rate of change of you calculated in (b)?

1. 👍 0
2. 👎 0
3. 👁 195
1. don't cheat

1. 👍 0
2. 👎 0
2. a) t=d/v = 0.5588 seconds

N=f*t = 650*0.5588= 363.235

b) i don't know it

c) f'= f* (1-(speed observer/speed sound))

1. 👍 0
2. 👎 0
3. jennifer for b I was thinking if we know N = ft and we derive this wouldn't it be the same f? I mean dN/dt = d(f*t)/dt that results in f. The other idea I had was calculating the wavelenght (lambda = v/f) using the sound velocity and the given f and then knowing lambda use it to find the new f that would result in the derivative given

1. 👍 0
2. 👎 0
4. from a we have:
N=f.d/Vs

for b:
N=f.(d+v.t)/Vs
dN/dt=f.v/Vs

1. 👍 0
2. 👎 0
5. but, how did you do with D)???

1. 👍 0
2. 👎 0
6. so I risked one chance and got:
a) N=f.d/Vs
b) dN/dt=f.Vobs/Vs
c) f'=f(1-Vobs/Vs)

and I thought for d:

f'=f.Vs/(Vs-Vwind)
but it's not right, I'll assume f' have to be bigger since, Vwind goes from source to observer.. but well, any suggestions?

1. 👍 0
2. 👎 0
7. I think that the fecuency remains the same in D. Because source and observer are at rest. By the same I mean that it could be 650 or the one you at c.

1. 👍 0
2. 👎 0
8. Look ellie you're right about b and c and d is 650 =)

1. 👍 0
2. 👎 0
9. for D, there is no relative speed, so whatever is gained by the wind at source is lost at observer (or vice versa), so no change

1. 👍 0
2. 👎 0
10. Let us now assume that both source and observer are at rest, but wind blows at a constant speed v=20 m/s in the direction source towards observer. By comparing the difference of the rate of wavefronts
leaving and wavefronts entering the region between source and observer, calculate the observed frequency f
′? (in Hz)no answer iqual

1. 👍 0
2. 👎 0

## Similar Questions

1. ### Science--HELP!!

1. In which of the following situations is a sound wave most likely to travel through air? A) An alarm clock rings in a vacuum. B) A giant star explodes. C) A grasshopper eats a leaf. D) An astronaut uses tools in space. 2. Which

2. ### Physics

Blood flow rates in the umbilical cord can be found by measuring the Doppler shift of the ultrasound signal reflected by the red blood cells. If the source emits a frequency f, what is the measured reflected frequency fR? Assume

3. ### Physics

A source passing a stationary observer is emitting a frequency of 560 Hz. If the speed of sound is 345 m/s, what must speed of the source be if the frequency speed is 480 hz? Here's what I've tried... Fo=480 Hz FObs = 480 + 560

4. ### physics

to an observer the pitch of the stationary source of the sound appears to be reduced by 20% if speed of sound is 340m/s then sped and direction of 5he observer is options 1.68 m/s away from the observer 2.96 m/s away from the

A source emits sound uniformly in all directions. There are no reflections of the sound. At a distance r1 from the source the sound is 6.5 dB louder than it is at a distance r2 from the source. What is the ratio r1/r2?

2. ### Physics

Three sources of sound are distributed along a line, as shown in the figure. v is the speed of sound. Source A is at rest, and it emits sound waves with a frequency of 480 Hz. Source B is traveling at v/5 to the right, and it

3. ### physics

The siren on an ambulance is emitting a sound whose frequency is 2421 Hz. The speed of sound is 343 m/s. (a) If the ambulance is stationary and you (the "observer") are sitting in a parked car, what are the wavelength and the

4. ### Science

6. Sonar is used to inspect pipelines and bridge foundations. In this scenario, sonar takes advantage of the fact that (1 point) A.sound waves can reflect.*** B.sound waves can diffract. C.sound waves can spread out. D.sound waves

1. ### physics

A stereo speaker represented by P in Figure 13-22 emits sound waves with a power output of 130.0 W. What is the intensity of the sound waves at point x when r = 7.8 m? W/m2

2. ### science

Sound waves are traveling through the air. Every ½ second, the sound waves pass a detector. Which of the following choices correctly describes the period and frequency of these waves? The period is 2 s, and the frequency is 2 Hz.

3. ### Physics doppler effect

A radar device emits microwaves with a frequency of 4.73E+9 Hz. When the waves are reflected from a van moving directly away from the emitter, the beat frequency between the source wave and the reflected wave is 751 beats per

4. ### phy

Doppler ultrasound is used to measure the speed of blood flow. If the speed of the red blood cells is v, the speed of sound in blood is u, the ultrasound source emits waves of frequency f, and we assume that the blood cells are