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!

Vector problem involving velocity and wind

  1. Sep 20, 2007 #1
    A 100-meter dash is run on a track in the direction of [tex]\vec{v} = 2\vec{e_{1}}+6\vec{e_{2}}[/tex] . The wind velocity [tex]\vec{e}_{1}+\vec{e_{2}}[/tex] km/h. The rules say that a legal wind speed measured in teh direction of the dash must not exceed 5 km/h. Will the race results be disqualified due to an illegal wind?

    I am unsure how to start this problem, any help would be great. I think that I must find the speed of the wind in that direction first, so finding that vector and then finding the magnitude of that vector. But I don't know how to find that vector.
  2. jcsd
  3. Sep 20, 2007 #2
    is the answer just projecting wind onto the velocity .
    proj v (w) = (w, v / v,v )v
    = ([5 1],[2 6] /[2 6],[2 6])[2 6]
    = ((10+6)/(4+36))[2 6]
    = 16/40 [2 6]
    = [4/5 12/5]

    so magnitude of that is around 2.52, so no the race won't be disqualified... am i doing somethin wrong. and should the 100-meter be incorporated somehow?
  4. Sep 20, 2007 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    No, the condition under which the race is disqualified says nothing about the length of the race, only the speed of the wind. Taking the projection of the wind vector onto the direction of the race is exactly right.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Vector problem involving velocity and wind
  1. Velocity vector (Replies: 5)