Direction of Displacement Vector [2D Kinematics]

1. Sep 27, 2008

stickyriceyum

1. The problem statement, all variables and given/known data

Question 1 [Correctly Solved]
A pedestrian moves 2.1km east and then 20km north. Find the magnitude of the resultant displacement vector. Answer in units of km.

Question 2
What is the direction of the displacement vector (using the counter-clockwise angular direction to be positive, within the limits of -180 degrees = 180 degrees)? Answer in units of degrees/

3. The attempt at a solution

[Theta] = (arctan) (Ay/Ax)
[Theta] = (arctan) 20km/2.1km = 1.466

------

I'm probably using the wrong equation. :x
(using the counter-clockwise angular direction to be positive, within the limits of -180 degrees = 180 degrees) Also, I don't understand what that means. Will someone please explain?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 27, 2008

abelanger

question #1: Draw it on a sheet of paper, make a Cartesian plane, use the upper y axis as north, right x-axis as east. You ll remember something!
*hint* Pythagorean Theorem ;)

Question #2: now im not sure if ill explain this right but! i think that this : "using the counter-clockwise angular direction to be positive, within the limits of -180 degrees = 180 degrees" means find the angle opposite to the 20km line (i think its the angle between the hypotenus and the 2.1km line)
Let's say it is ;)
now remember SOHCAHTOA and see if you can do it.

Got more questions, just PM me. Goodluck!