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How did the book get this answer? Please help with motion!

  1. Apr 2, 2008 #1
    1. The problem statement, all variables and given/known data
    A ship is 8km from a coastline that stretches in a east west direction. The navigator on the ship records that the lighthouse on the coastline has a bearing of N 27 E. After sailing for 30 minutes the navigator records that the lighthouse is 15km due north.

    a) What is the displacement of the ship between the two recordings?
    b) What is the ships average velocity?

    2. Relevant equations
    a^2 + b^2=C^2
    v=X/t
    v=u+at


    3. The attempt at a solution
    Horizontal displacement:
    x= 8tan27
    horizontal displacement = 4.08km

    Find displacement via Pythagorus:
    x^2 = a^2+b^2
    x^2= 4.08^2 + 7^2
    Displacement = 8.10 km = WRONG, Right= 9.2km

    How is the above answer possible, as I have worked this question out many different ways and still not got this answer.

    Could someone please assist me with this problem?

    I have attached my freebody diagram (I dont posses very good Paint skills)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

    Last edited: Apr 2, 2008
  2. jcsd
  3. Apr 2, 2008 #2

    Dick

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    Um, even though you didn't actually state the question, if it's what I think it is, I agree with your answer.
     
  4. Apr 2, 2008 #3
    Thank you for noticing - Ive fixed it now :)

    The question was about the ships displacement.
     
  5. Apr 2, 2008 #4

    Dick

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    Right. Then I definitely agree with your answer.
     
  6. Apr 2, 2008 #5
    Thank you for your answer - I was quite perplexed by their answer, Im glad Im right. :D

    Thanks for your help, I really appreciate it! Its great to know that I can get some support with physics, outside of school.

    Kindest Regards,
    TheKovac
     
  7. Apr 3, 2008 #6

    tiny-tim

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    … wrong bearing …

    Hi everyone!

    I think the book was working on a bearing of N 37 E. :frown:
     
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