Sound intensity decreases when amplification (volume) decreases.
i would have to say because a person/animal can only hear so well and only from a limited distance, therefore a noise further away is harder to hear.
Yes.
No, it follows the inverse square law. That is, the intensity is inversely proportional to the square of the distance. I2/I1 = (r1/r2)². Intensity decreases with 1/r² from increased distance, while...
If r is the distance from the sound source the sound intensity drops with (1/r)².