# Parallel and perpendicular part of a vector

1. Sep 3, 2013

### cytochrome

1. The problem statement, all variables and given/known data
Resolve the force F into

a) a part perpendicular to AB and

b) a part parallel to BC

2. Relevant equations
a dot b = ab*cos(θ)

3. The attempt at a solution
I attached my attempt in the .pdf file. For some reason it is wrong. I don't understand how my reasoning is incorrect.

The orange square in the picture is a supposed to be a wooden box in the problem, so that detail is not important to the problem.

File size:
186.6 KB
Views:
180
2. Sep 3, 2013

### SteamKing

Staff Emeritus
First, you might want to check the angle given by arctan (3/5).

3. Sep 3, 2013

### cytochrome

Thanks for pointing that out, but the answer still comes out to be wrong even if I change that. Am I setting up the problem wrong?

Do you do F*cos(θ) to find a parallel component of F and F*sin(θ) to find a perpendicular part of F in general?

4. Sep 3, 2013

### Staff: Mentor

Are you sure that your initial diagram is correct? The given answers do not seem to match the diagram.

Yes.

5. Sep 3, 2013

### cytochrome

Yes my diagram is correct. It's possible the solutions could be wrong, it's out of an old book... Anyways, I was wondering if my methodology was correct.