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Unformatted text preview: khounvivongsy (sk27799) – Practice Problems 2 Solutions – Weathers – (17104) 1 This printout should have 36 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 3) 10.0 points You dip your finger into a pan of water twice each second, producing waves with crests that are separated by 0 . 14 m. Determine the frequency of these water waves. Correct answer: 2 Hz. Explanation: Let : n = 2 vibrations and Δ t = 1 s . f = number of vibrations Δ t = 2 1 s = 2 Hz . 002 (part 2 of 3) 10.0 points Determine the period of these water waves. Correct answer: 0 . 5 s. Explanation: T = 1 f = 1 2 Hz = . 5 s . 003 (part 3 of 3) 10.0 points Determine the speed of these water waves. Correct answer: 0 . 28 m / s. Explanation: Let : λ = 0 . 14 m . v = f λ = (2 Hz)(0 . 14 m) = . 28 m / s . 004 10.0 points The distance between two successive crests of a certain transverse wave is 1 . 33 m. Eight crests pass a given point along the direction of travel every 18 . 3 s. Calculate the wave speed. Correct answer: 0 . 581421 m / s. Explanation: Let : λ = 1 . 33 m , n = 8 crests , and Δ t = 18 . 3 s . v = f λ = n Δ t λ = 8 18 . 3 s (1 . 33 m) = . 581421 m / s . keywords: 005 10.0 points Earthquakes produce two kinds of seismic waves: The longitudinal primary waves (called P waves) and the transverse secondary waves (called S waves). Both S waves and P waves travel through Earth’s crust and mantle, but at different speeds; the P waves are always faster than the S waves, but their exact speeds depend on depth and location. For the pur pose of this exercise, we assume the P wave’s speed to be 8680 m / s while the S waves travel at a slower speed of 5080 m / s. Suppose a seismic station detects a P wave and then 78 . 7 s later detects an S wave. How far away is the earthquake center? Correct answer: 963 . 953 km. Explanation: Let : v P = 8680 m / s , v S = 5080 m / s , and Δ t = 78 . 7 s . Suppose the earthquake happens at time t = 0 at some distance d . The P wave and the khounvivongsy (sk27799) – Practice Problems 2 Solutions – Weathers – (17104) 2 S wave are both emitted at the same time t = 0, but they arrive at different times, re spectively t P = d v P and t S = d v S . The S wave is slower, so it arrives later than the P wave, the time difference being Δ t = d v S − d v P = d ( v P − v S ) v P v S . Consequently, given this time difference and the two waves’ speeds v P and v S , we find the earthquake center being d = v P v S Δ t v P − v S = (8680 m / s) (5080 m / s) (78 . 7 s) (8680 m / s) − (5080 m / s) · 1 km 1000 m = 963 . 953 km . away from the seismic station....
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This note was uploaded on 05/09/2010 for the course PHYS 1710 taught by Professor Weathers during the Spring '09 term at University of North Carolina Wilmington.
 Spring '09
 weathers
 mechanics

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