Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Vector angles and velocity

  1. Feb 18, 2004 #1
    HELP please: vector angles and velocity

    Alright i don't nessesarily need an answer for this but maybe just a way to set it up. The problem is worded weird and no one can figure it out.

    A passenger walks from one side of the ferry to the other side as it approaches a dock. If the passenger's velocity is 1.2 m/s due north relative to the ferry, and 4.5 m/s at an angle of 35 degrees west of north relative to the water, what are the direction and magnitude of the ferry's velocity relative to the water?

    (blank) degrees west of north
    (blank) m/s
    Last edited: Feb 18, 2004
  2. jcsd
  3. Feb 19, 2004 #2


    User Avatar
    Science Advisor
    Gold Member

    You just have to do some vector addition.

    [tex] \vec v_{f/w} + \vec v_{m/f} = \vec v_{m/w} [/tex]

    where f = ferry, w = water, and m = man, and / = with respect to.

    Drawing the triangle formed by the three vectors may help. Can you take it from there?
  4. Feb 19, 2004 #3
    The passenger's velocity relative to the water equals the vector sum (the resultant) of her velocity relative to the ferry plus the ferry's velocity relative to the water.

    Pw = Pf + Fw

    In your problem Fw is the unknown. Set up a diagram illustrating this vector addition & solve it using simple trig.
  5. Feb 19, 2004 #4
    How does this keep happening James?:smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook