The sound intensity from a jack hammer breaking concrete is 2.00 W/m2 at a distance of 2.00 m from the point of impact. This is sufficiently loud to cause permanent hearing damage if the operator doesn’t wear ear protection. What is the sound intensity for a person watching from “20”.0 m away?
We know that intensity of sound is inversely proportional to square of distance of point from the source .
For two points at distance of R₁ and R₂ , Intensity of sound I₁ and I₂ will vary as follows
I₁ / I₂ = R₂² / R₁²
I₁ = 2 W / m² , R₁ = 2 m , R₂ = 20m , I₂ = ?
Putting the values in the expression above
2 / I₂ = 20² / 2²
I₂ = (2 x 4) / 400
= .02 W / m²