1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Geometry/Discrete Math Velocity Vectors Help

  1. Feb 12, 2006 #1
    I'm working on this problem and it's frustrated me and I was wondering if I could get a spot of help on it:

    An airplane heads due south with an air speed of 480km/h. Measurements made from the ground indicate that the plane's ground speed is 528 km/h is 528 km/h at 15 degrees east of south. Calculate the wind speed.

    I have a diagram of what I worked out so maybe someone could show me what I did right and what I did wrong, that'd be nice.

    http://img497.imageshack.us/img497/6442/diag0ia.png [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Feb 12, 2006 #2


    User Avatar
    Homework Helper

    You've got your plane heading 15 deg south of east, not 15 deg east of south!
    15 deg east of south is at -75 degrees( that's 75 degrees clockwise from direction of the positive x-axis)
  4. Feb 12, 2006 #3
    Okay thanks. I'll try it again and see what I come up with.
  5. Feb 12, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    I would suggest using -j (-y) for S, and i (+x) for E.

    Consider the ground speed as the true speed. Resolve the ground speed vector into its S and E components. The air speed is 480 km/h, so the air must have a southward component to carry the plane with a faster ground speed.

    What are the S and E components of the ground speed vector?
  6. Feb 12, 2006 #5
    I figured it out. The problem were in the angles, so I redrew it like this:

    http://img490.imageshack.us/img490/842/diag3tf.png [Broken]

    Then I used cosine law to get the wind speed. Just thought I'd post the solution so people would know :D
    Last edited by a moderator: May 2, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook