[Soundwaves] Energy and decibel

[hiuting]

Homework Statement

The sound level in a noisy classroom is 101 dB. How much energy in J is transmitted to the outside through an open window of height 2 m and width 2.75 m, if the class is 40 minutes long?. What is the decibel rating 1 km from the classroom, assuming sound is distributed equally in all directions?

Homework Equations

I = P / 4(pi)r²
\beta = 10log(I/I₀)

The Attempt at a Solution

the answers are [P = 0.069 W; E = 166 J; 46.4 dB]

I tried finding v, but I don't know what the dimensions of the window are for.

 

[alphysicist]

Hi hiuting,

Homework Statement

The sound level in a noisy classroom is 101 dB. How much energy in J is transmitted to the outside through an open window of height 2 m and width 2.75 m, if the class is 40 minutes long?. What is the decibel rating 1 km from the classroom, assuming sound is distributed equally in all directions?

Homework Equations

I = P / 4(pi)r²

This is the intensity in some cases, but what is the definition of intensity?

\beta = 10log(I/I₀)

The Attempt at a Solution

the answers are [P = 0.069 W; E = 166 J; 46.4 dB]

I tried finding v,

What v are you trying to find, and how did you use the above equations to find it?

but I don't know what the dimensions of the window are for.