Giancoli 7th Edition textbook cover
Giancoli's Physics: Principles with Applications, 7th Edition
11
Vibration and Waves
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11-1 to 11-3: Simple Harmonic Motion
11-4: Simple Pendulum
11-7 and 11-8: Waves
11-9: Energy Transported by Waves
11-11: Interference
11-12: Standing Waves; Resonance
11-13: Refraction
11-14: Diffraction

Question by Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014, Reprinted by permission of Pearson Education Inc., New York.
Problem 44
Q

What is the ratio of

  1. the intensities, and
  2. the amplitudes, of an earthquake P wave passing through the Earth and detected at two points 15 km and 45 km from the source?
A
  1. 0.110.11
  2. 0.330.33
Giancoli 7th Edition, Chapter 11, Problem 44 solution video poster
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VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. Since the earthquake spreads out spherically from the epicenter that means these equations apply where you take intensity at position 2 divided by intensity at position 1, and it equals the distance from the epicenter to position 1 squared over the distance to position 2 squared. So, that's 15 kilometers squared divided by 45 kilometers squared. No need to convert this into meters since it's a ratio and the only thing that's important is that the units are the same, so they cancel. And we'll be left with 0.11. So, the intensity at position 2 is 11% of the intensity at position 1. As for the amplitudes, amplitude 2 over amplitude 1 equals r1 over r2. So, that's 15 over 45. So, amplitude 2 will be 33% of the amplitude at position 1.

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