Results 1 to 2 of 2

Math Help - bearing

  1. #1
    Member
    Joined
    Dec 2007
    Posts
    80

    bearing

    Im not sure how to draw this and so i havnt been able to try and solve it yet, so if you could help me draw it and give a few hits that would be great thnx

    A ship travelling with a constant speed and direction is signhted from a lighthouse.At this time it's 2.7kn away on a bearing of 42degrees. half an hour later it is ona bearing of 115degrees at a distence of 7.6 km from the same lighyhouse. find its speed in km per hour

    thank you
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,662
    Thanks
    603
    Hello, Chez_!

    A ship travelling with a constant speed and direction is signhted from a lighthouse.
    At this time it's 2.7km away on a bearing of 42.
    Half an hour later, it is on a bearing of 115 at a distence of 7.6 km.
    Find its speed in km per hour
    Code:
          N       A
          :       *
          : 42 *  \
          :   *2.7  \
          : *        \
        L * 73       \ x
             *         \
                *       \
                7.6*     \
                      *   \
                         * \
                            * B
    Bearings are measured clockwise from North.

    The lighthouse is at L.

    The ship is first sighted when \angle NLA = 42^o,\;LA = 2.7\text{ km}

    The ship is sighted next when \angle NLB = 115^o\quad\Rightarrow\quad \angle ALB = 73^o
    . . and LB = 7.6\text{ km}

    We want the distance: x \:=\:AB


    In \Delta ALB, use the Law of Cosines:
    . . x^2 \;=\;2.7^2 + 7.6^2 - 2(2.7)(7.6)\cos73^o \;=\;53.05106524

    Hence: . x \;=\;7.28361622\text{ km}

    Now you can calculate its speed, right?

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. bearing
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: September 6th 2010, 11:41 AM
  2. Bearing issues!
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 20th 2010, 08:51 AM
  3. bearing
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: December 7th 2008, 06:31 AM
  4. Bearing Help
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: January 6th 2008, 05:11 AM
  5. bearing
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 22nd 2006, 05:25 AM

Search Tags


/mathhelpforum @mathhelpforum