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Swimmer from shore?

  1. Feb 14, 2007 #1
    1. The problem statement, all variables and given/known data
    At a particular time, a long distance ocean swimmer is 5km from a coast line that stretches in a north south direction. One of the passengers on the boat accompanying the swimmer determines that a lighthouse on the coastline has a bearing of N70E. After 30 minutes the swimmer is 5km due west of the lighthouse.
    a) What is the displacement of the swimmer between the two measurements?
    b) What is the average velocity of the swimmer?

    2. Relevant equations

    3. The attempt at a solution
    I drew a diagram with this question but if going according to the scenario, it would mean the swimmer ends up on the other side of the shore. But how thick is the shore? I don't think my diagram is correct. Should the last sentence contain the word east instead of west?
  2. jcsd
  3. Feb 14, 2007 #2


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    Homework Helper

    No, I think it is correct. I think it means the swimmer is 5 km west from the point of view of the lighthouse, not the other way around.
  4. Feb 14, 2007 #3
    In that case, the swimmer hasn't changed position longitudinally (i.e. still 5km from the coastline). Simple trig shows that the displacement is 1.82km with tan(70)=5/x => x=1.82 which is what the answers suggested. So thats that figured out.
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