The sound intensity from a jackhammer breaking concrete is 2

The sound intensity from a jackhammer breaking concrete is 2.00 W/m^2 at a distance of 2.00 m from the point of impact. The sound intensity for a person watching from a distance of 30.0 m away closest to: (a) 12.8 times 10^-3 W/m^2 (b) 8.89 times 10^-3 W/m^2 [c] 6.53 times 10^-3 W/m^2 (d) 5.00 times 10^-3 W/m^2 (e) 3.95 times 10^-3 W/m^2

Solution

Acccording to the given problem,

First, the sound intensity (I) is given by the formula

I=P/(4r²)

Now, rearange the equation and calculate the Power.

P=4Ir²

As given I = 2.0 W/m² at r = 2.0m we have

P=4*2.0 W/m²*(2m)²

P=100.531W

Now solve I at r = 30m

I = P/(4r²)

I =(100.531W)/[4*(30m)²]

I 8.889 x 10^-3 W/m²

[B]