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Homework Help: Time Speed problems

  1. Sep 12, 2005 #1
    Ok well i've had a bit of trouble understanding this question

    The velocity of the transverse waves produced by an earthquake is 6.17 km/s, while that of the longitudinal waves is 10.3039 km/s. A seismograph records the arival of the transverse waves 60.8 s after that of the longitudinal waves.
    How far away was the earthquake? Answer in units of km

    Yea i guess i just don't understand the way it's setup or something.
  2. jcsd
  3. Sep 13, 2005 #2


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    Homework Helper

    We do ask that you show an attempt at a problem, but:

    We assume that the waves started at the same point at the same time. You know the difference in speeds. Given that, if you assume they travelled for an hour, you could figure out how far ahead the faster was than the slower, right? From that, you could figure out how long it would take for the slower wave to reach the point where the faster wave is. All you really have to do is work it backwards from there.

    Does that help?
  4. Sep 13, 2005 #3
    Treate that both rays are like objects that start from a common point , their velocities are given which remain constant , and the difference in arrival times at a distance 's' are given . Apply Translational Kinematics and show your work.

  5. Sep 13, 2005 #4


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    Since you are asked "How far away was the earthquake?", let D= distance to the earthquake, in km. The information you are given concerns time. How is time related to distance? Well, speed equals distance over time and you are told the speed- from s= D/t, t= D/s. For transverse waves speed= 6.17 km/s so to travel distance D requires D/6.17 seconds. For longitudinal waves speed 10.3039 km/s (it seems strange that they would give one speed to 3 significant figures and the other to 6!) so to travel distance D requires D/10.3039 seconds. You are told that the DIFFERENCE between those two times is 60.8 seconds.
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