Homework Help: college physics

Posted by Anonymous on Tuesday, April 27, 2010 at 10:33am.

The intensity of an earthquake wave passing through the Earth is measured to be 2.5×10^6 J/m^2 at a distance of 43 km from the source. What was its intensity when it passed a point only 2.0 km from the source? AND At what rate did energy pass through an area of 4.0 m^2 at 2.0 km? Really need help with this problem please!!!

college physics - drwls, Tuesday, April 27, 2010 at 11:38am
Use the inverse square law. "intensity" is the total energy in the seismic wave per unit area.

2 km is 43/2 = 21.5 times closer than 43 km. Intensity will increase by a factor 21.5^2 = 462. (That's where the inverse-square law comes in). The intensity at 2 km is therefore 1.15*10^9 J/m^2. Multiply that by 4 m^2 for the total energy through that area. That will be a lot of energy. Billions of Joules would probably destroy any building located there

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