1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relative motion of two ships

  1. Sep 28, 2004 #1
    Ships A and B leave port together. For the next two hours, ship A travels at 35.0 mph in a direction 25.0 degrees west of north while the ship B travels 80.0 degrees east of north at 30.0 mph.
    What is the distance between the two ships two hours after they depart?
    What is the speed of ship A as seen by ship B?

    basically i tried using trig to find the x component of both vectors and then added them. it wanted distance at t = 2 so i did 70 * sin (25) + 60 * sin(80) but it was incorrect. i tried this method with the example in the book and it was fairly close. so im guessing i did it incorrectly but got an answer that was close by coincidence? and for the second part im really unsure where to begin, i just know reference frames have something to do with it and maybe some sort of vector addition/subtraction. any suggestions will be much appreciated.
    Last edited: Sep 28, 2004
  2. jcsd
  3. Sep 28, 2004 #2
    anyone help please? im stuck
  4. Sep 28, 2004 #3


    User Avatar
    Homework Helper

    try using

    [tex] v = \frac{d}{t} [/tex]
  5. Sep 28, 2004 #4
    i got it using the law of cosines. thanks for your suggestion though.
  6. Sep 28, 2004 #5


    User Avatar
    Science Advisor
    Homework Helper

    When you're calculating the lenght of a component-wise vector it's
    from the way you describe what you did, you might have forgotten the [tex]y[/tex] component.

    The second part looks like straightforward vector addition as well.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Relative motion of two ships