Distance of building related to echo

In summary, the motorist will hear an echo from the nearest building 1 s after he hit the horn, and the second echo will come from the further building.
  • #1
songoku
2,266
319

Homework Statement


A road lies between two parallel buildings. A motorist travels with speed 36 km/h on the road and hits the horn. He heard the echo 1 second later. The speed of sound is 330 m/s
a. Find the distance of the building
b. When will he hear the second echo?

Homework Equations


2d = v.t


The Attempt at a Solution


The first echo will come from the nearest building and the second echo will come from the further building.

a. the distance of nearest building to motorist = d1
2 d1 = v.t
d1 = 115 m


I don't know how to find the distance of further building to the motorist and is the speed of motorist being used in the calculation?

Thanks
 
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  • #2
songoku said:

Homework Statement


A road lies between two parallel buildings. A motorist travels with speed 36 km/h on the road and hits the horn. He heard the echo 1 second later. The speed of sound is 330 m/s
a. Find the distance of the building
b. When will he hear the second echo?

Homework Equations


2d = v.t


The Attempt at a Solution


The first echo will come from the nearest building and the second echo will come from the further building.

a. the distance of nearest building to motorist = d1
2 d1 = v.t
d1 = 115 m


I don't know how to find the distance of further building to the motorist and is the speed of motorist being used in the calculation?

Thanks

Try to imagine you are the motorist, traveling on the road in between two parallel buildings. What do you mean on "nearest" and "further" building? Show the path of the sound that hits the ears of the motorist in a figure.

ehild
 
  • #3
ehild said:
Try to imagine you are the motorist, traveling on the road in between two parallel buildings. What do you mean on "nearest" and "further" building? Show the path of the sound that hits the ears of the motorist in a figure.

ehild

untitled-12.jpg


Let P be the motorist and there are two parallel buildings on his right and left side. The nearest building is the right one and the further building is the left one. The motorist moves "into the page" with respect to the reader (same as (×) sign of magnetic field)

The sound will hit the right building first and being reflected to his ear. Sound will also be reflected by the left building and he will hear the second echo.

But I don't know how to calculate the distance...
 
  • #4
I'd say the intention is that the road follows a path exactly midway between the buildings.
 
  • #5
NascentOxygen said:
I'd say the intention is that the road follows a path exactly midway between the buildings.

Oh I see, the distance is twice of what I've calculated. So the speed of the motorist is not important?

Thanks
 
  • #6
songoku said:
Oh I see, the distance is twice of what I've calculated. So the speed of the motorist is not important?

Thanks
The motorist will be in a different location each time an echo reaches his ears, so I'd say you do have to take into account his movement. I'm picturing it as the motorist in an open-top sports car reaching up and firing a starter's pistol as he passes between the buildings (or as he drives through a canyon with steep sides). How long before the radiating pressure wave gets back to him in some form?
 
  • #7
NascentOxygen said:
The motorist will be in a different location each time an echo reaches his ears, so I'd say you do have to take into account his movement. I'm picturing it as the motorist in an open-top sports car reaching up and firing a starter's pistol as he passes between the buildings (or as he drives through a canyon with steep sides). How long before the radiating pressure wave gets back to him in some form?

I am not sure, maybe 1 second because that is the time needed for him to hear an echo.
 
  • #8
To make easier to imagine, see picture. The motorist drives just in the middle of the road between the pair of long buildings, at distance D from both, with speed V=36 km/h. He hits the horn: the sound travels in every direction and reaching the wall of the buildings, reflects. A narrow beam of sound wave reaches the middle of the road just as the motorist also reaches there, Δt=1 s later as the horn was hit. The motorist traveled S=VΔt distance. How long distance traveled the sound during that time if the speed of sound is 330 m/s? The path of the sound and that of the motorist make an isosceles triangle. What is D then?

ehild
 

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  • #9
The distance traveled by the motorist in interval 1 s = 10 m
The distance traveled by the sound in interval 1 s = 330 m

D = √(52 + 1652) = 165.076 m

a. distance between building = 2D

b. he will hear the second echo 1 s later ??

Thanks
 
  • #10
songoku said:
The distance traveled by the motorist in interval 1 s = 10 m
The distance traveled by the sound in interval 1 s = 330 m

D = √(52 + 1652) = 165.076 m

a. distance between building = 2D

b. he will hear the second echo 1 s later ??

Thanks

Check it. Is D the hypotenuse?

ehild
 
  • #11
ehild said:
Check it. Is D the hypotenuse?

ehild

Oh yes, I see my mistake.

For answer (b), am I correct? I think the answer will be 1 s because the motorist and sound undergo uniform motion
 
  • #12
Yes, of course, the second echo follows the first one after 1 s.

ehild
 
  • #13
ehild said:
Yes, of course, the second echo follows the first one after 1 s.

ehild

Thanks for the help :smile:
 

1. What is an echo and how is it related to the distance of a building?

An echo is the reflection of sound waves off of a surface. The distance of a building can affect the echo because the sound waves will travel a longer distance before reaching a reflective surface, resulting in a longer delay between the original sound and the reflected sound.

2. Does the material of a building affect the distance of an echo?

Yes, the material of a building can affect the distance of an echo. Hard and smooth surfaces, such as concrete or glass, will reflect sound waves better and result in a longer distance of the echo compared to softer or rougher surfaces, which may absorb more sound waves.

3. How does the shape of a building impact the distance of an echo?

The shape of a building can affect the distance of an echo. A curved or angled surface can cause sound waves to reflect in different directions, potentially creating a longer or shorter distance for the echo. A building with more flat surfaces may result in a more direct and shorter echo.

4. Can the distance of a building affect the intensity of an echo?

Yes, the distance of a building can impact the intensity of an echo. Sound waves will lose energy as they travel a longer distance, resulting in a weaker and more diffuse echo. This means that the further the distance of a building, the less intense the echo will be.

5. How does the environment surrounding a building impact the distance of an echo?

The environment surrounding a building can affect the distance of an echo. Open and empty spaces will allow sound waves to travel further, resulting in a longer distance of the echo. In contrast, a crowded or cluttered environment may absorb more sound waves and result in a shorter distance of the echo.

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