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**"Answer This" Questions**

**Chapter 5**

**5-A.
I ntensity versus distance**

Suppose you hear a firecracker go off 60 feet away from you. The intensity
you hear is 0.09 Watts/m^{2}. What intensity would a person
who is standing 20 feet away hear?

a) 0.81 Watts/m^{2}

b) 0.27 Watts/m^{2}

c) 0.09 Watts/m^{2}

d) 0.03 Watts/m^{2}

e) 0.01 Watts/m^{2}

**Answer:**

The
intensity changes as the square of the distance. Thus, if the distance
is three times closer, as it is here (60/20 = 3), the intensity is 3^{2}
= 9 times as much. Since 0.09x9=0.81 W/m^{2}, the answer is
a).

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©
William J. Mullin