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Quiz1sol

# Quiz1sol - confirms that the earthquake came from San...

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Physics 7C Quiz 1 solution 1) Uh oh, the ground is shaking. You suspect an earthquake in San Francisco, 100 km away. You feel the ground moving with a peak to peak motion of 1 cm toward and away from the direction of San Francisco, with about 5 cycles per second. Fortunately, your geologist friend reminds you that seismic P-waves (longitudinal) travel at 5 km per second. Write the wave equation for the P-waves. We must find the amplitude, period, and wavelength. We don’t have enough information to determine the phase constant, so we’ll set it to zero. We will also set our initial position to zero. The function y measures the displacement in the direction of San Francisco. ) 1 2 2 . 0 2 sin( 5 . 0 ) ( 1 2 . 0 5 2 . 0 5 1 1 5 . 0 km x s t cm t y km s s km T v s Hz f T cm A - = = = = = = = = π π λ 2) Your geologist friend also informs you that S-waves (transverse, up and down) travel at approximately half the speed of P-waves. The bouncing you feel 20 seconds later
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Unformatted text preview: confirms that the earthquake came from San Francisco. Given the P-wave and S-wave have the same source, explain which parameters in the wave equation will change, and which must remain the same. The variable y will no longer represent the displacement in the same direction as the wave is traveling, but instead represent the displacement up-and-down. Because the wave source is the same, the frequency will also be the same. The same argument could be made about amplitude, but it doesn’t account for a source moving different magnitudes in different directions, or energy density, or different directions, so nothing need be said about amplitude. The velocity has changed while the frequency has stayed the same, so the wavelength must change, because wavelength is the product of velocity and period....
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