Find Sound Power of Motor Car - 0.354 W

In summary, the conversation is about a homework assignment involving sound waves and calculating the sound power of a motor car at a distance of 7.5m. The steps involved include finding the sound intensity and using it to calculate the power, but there is a discrepancy between the student's answer and the teacher's answer. The mistake in the calculation was found to be the direction of the sound energy, which should reflect off the ground rather than travel downward.
  • #1
Clari
62
0
Hello! I am doing some questions about sound waves for my homework assignment and have some problem in one of them.
Assuming that it radiates sound uniformly, find the sound power from a motor car whose sound level at a distance of 7.5m is 87dB.
Here are my steps:
I = sound intensity, I_0 = minimum audible intensity
By h = 10log(I/I_0)
87 = 10 log (I / 10x10^-12)
I = 5.01 x 10^-4 W/m^2
By I = P / 4 pi r^2
5.01x 10^-4 = P / 4 pi 7.5^2
P = 0.354W
But the answer given by my teacher is 0.18W...Can anyone tell me what's wrong in my calculation.:smile: Thanks!
 
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  • #2
I also got P = 0.354W.
 
  • #3
You were having the Sound Energy travel downward, into the ground.
Almost all the sound will reflect from the solid Earth -
spreading over the upper (air) hemisphere, 2 pi r^2 .
 

What is the purpose of finding the sound power of a motor car?

The sound power of a motor car is an important measurement that helps determine the level of noise pollution produced by the vehicle. It can also provide information about the engine's efficiency and any potential mechanical issues.

How is the sound power of a motor car measured?

The sound power of a motor car is typically measured using a sound level meter, which records the intensity of sound at various frequencies. The measurements are then converted into decibels (dB) and can be compared to established standards for noise pollution levels.

What factors can affect the sound power of a motor car?

The sound power of a motor car can be affected by a variety of factors, including the type and condition of the engine, the exhaust system, the speed of the vehicle, and the surrounding environment. Different driving conditions, such as acceleration or idling, can also impact the sound power.

How can the sound power of a motor car be reduced?

To reduce the sound power of a motor car, various measures can be taken such as using noise-cancelling technology, improving the insulation and design of the vehicle, and regularly maintaining the engine and exhaust system. Additionally, driving at lower speeds and avoiding sudden accelerations can also help reduce noise pollution.

Are there any regulations or standards for the sound power of motor cars?

Yes, there are regulations and standards in place to control the sound power of motor cars. In the United States, the Environmental Protection Agency (EPA) has established noise emission standards for motor vehicles, and most countries have similar regulations in place. These standards help ensure that motor cars do not produce excessive levels of noise pollution.

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