posted by .

You are traveling in a car toward a hill at a speed of 40.8 mph. The car's horn emits sound waves of frequency 243 Hz, which move with a speed of 340 m/s.The frequency with which the waves strike the hill is 254.7Hz and the frequency of the reflected sound waves you hear 271.2 Hz.
What is the beat frequency produced by the direct and the reflected sounds at your ears?

271.2-243 is not the correct answer

actually,it is. they may want the sum frequency, in mixing two sound, one gets the sum and difference.

could you help me more with this?

The question is misleading I think. I gave the obvious answer as well yesterday Bob but it is not what they want.
It says you hear 271.2 Hz coming back from the hill, but I think it may mean that the frequency of the waves reflected is 271,2 and you will hear a higher frequency in the moving car.
The 271.2 is from a stationary source and you are approaching it at 40.8 mph which is 18.2 meters/s
fl = (v+vl) fs/v = (340+18.2)271.2/340
= 285.7
so the two frequencies you hear in the car are
285.7 and 243
and the beat is 42.7 Hz

I am sorry..but this is not the right answer either

Ah well I surrender ! I think the problem is English, not Physics.

I assume that you are plugging into so computer , try rounding to 43 Hz

Hey, are you sure those waves do not hit the hill at 256.7, not 254.7 ??
vl = 340 * 243/(340-18.2)

yes they hit it at 256.7..i typed it wrong...i am still not getting the correct beat frequency

Well they hit the hill at 256.7 and come back at that same frequency in the air.
Now an observer in the car will hear them at:
256.7(340+18.2)/340 = 270.4
not 271.2
so I get
271.2 - 243 = 28.2

• typo -

Excuse me
270.4 - 243 = 27.4 !!!

That question was poorly written and riddled with errors. Burn the book :)

thank you soooo much...the answer is correct..thanks again for working on it for this long

You are welcome, like I said sacrifice that book to some deity !

## Similar Questions

1. ### physics

1)As a sound source moves away from a stationary observer, the number of waves will. decrease 2)How fast should a car move toward you for the car's horn to sound 2.88% higher in frequency than when the car is stationary?
2. ### physics

1)As a sound source moves away from a stationary observer, the number of waves will. decrease 2)How fast should a car move toward you for the car's horn to sound 2.88% higher in frequency than when the car is stationary?
3. ### physics

1)As a sound source moves away from a stationary observer, the number of waves will. A)increase B)decrease C)remain the same D)need to know the speed of the source (answer:decrease.) As the detector recedes from the source, the relative …
4. ### Physics

1)As a sound source moves away from a stationary observer, the number of waves will. A)increase B)decrease C)remain the same D)need to know the speed of the source (answer:decrease.) As the detector recedes from the source, the relative …
5. ### physics

You are traveling in a car toward a hill at a speed of 40.8 mph. The car's horn emits sound waves of frequency 243 Hz, which move with a speed of 340 m/s.The frequency with which the waves strike the hill is 254.7Hz and the frequency …

You are traveling in a car toward a hill at a speed of 40.8 mph. The car's horn emits sound waves of frequency 243 Hz, which move with a speed of 340 m/s.The frequency with which the waves strike the hill is 254.7Hz and the frequency …
7. ### physical

You are traveling in a car toward a hill at a speed of 42.1 mph. The car's horn emits sound waves of frequency 251 Hz, which move with a speed of 343 m/s. a) Determine the frequency with which the waves strike the hill. b) What is …
8. ### 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 emits …
9. ### Physics

A stationary observer hears a sound with a frequency of 450 Hz from an approaching car. If the car emits the sound at a frequency of 360 Hz, what would be the speed of the car?
10. ### physics

A police car siren emits a sound wave with a frequency fs = 400 Hz and it is moving toward the wall at 25 /m/s. What frequency reflected from the wall does the driver of the police car hear ?

More Similar Questions