(a) What is the ratio of the intensity of an earthquake wave as it passes a poin

Physics
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(a) What is the ratio of the intensity of an earthquake wave as it passes a point 20 km from the source to the intensity as it passes a point 15 km from the source?

 
(b) What is the ratio of the amplitude of an earthquake wave as it passes a point 20 km from the source to the amplitude as it passes a point 15 km from the source?
Apr 1st, 2015

If we assume the energy spreads out equally in all directions, the intensity obeys the inverse square law.
(a) Distance increases by a factor of 20/15 = 1.33
Intensity reduces by 1.33² = 1.77
Ratio of intensities is 1/1.77 =0.56
(b) The intensity is proportional to amplitude squared, so amplitude is proportional to the square root of intensity. √1.77 = 1.33
Ratio of amplitudes is 1/1.33

Apr 1st, 2015

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