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!

Decomposing vectors

  1. Aug 30, 2015 #1
    1. The problem statement, all variables and given/known data
    The magnitude of the vector is 6 m, and points 35 degrees north of west. Find the x component of the vector.

    2. Relevant equations

    x = |R|cos(theta)

    3. The attempt at a solution

    I am confused about what degrees to input into the cosine function. I know that the vector is pointing 35 degrees north of west, which means that the x component will be negative, but there are two ways I could do it am I am not sure which one I should do. First, I could tack on a negative and calculate -(6 m)cos35 = -4.9 m. Another way is not tack on a negative and calculate (6 m)cos145 = -4.9 m. Which method is better, and which one should I use on a regular basis?
  2. jcsd
  3. Aug 30, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    Both ways are fine, as long as you don't try to memorize a rule and blindly apply it. Personally, I like the first approach, and just tack on the negative sign when I know there should be one.
  4. Aug 30, 2015 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Well, you could learn the angles for the cardinal points of the compass, but why do that when you can just make something up?

    East = 0°
    North = 90°
    West = 180°
    South = 270°
  5. Aug 30, 2015 #4
  6. Aug 31, 2015 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You've never seen the following diagram (or a similar one)?:


    It should have been used when you studied trigonometry.

    After all,
    cos (0°) = 1.0
    sin (0°) = 0.0

    cos (90°) = 0.0
    sin (90°) = 1.0

    cos (180°) = -1.0
    sin (180°) = 0.0

    cos (270°) = 0.0
    sin (270°)= -1.0

    etc., etc.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Decomposing vectors
  1. Vectors vector (Replies: 4)