# Parallel and perpendicular part of a vector

## Homework Statement

Resolve the force F into

a) a part perpendicular to AB and

b) a part parallel to BC

## Homework Equations

a dot b = ab*cos(θ)

## 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.

#### Attachments

• Problem.pdf
186.6 KB · Views: 364

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

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

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?

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

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?
Yes.

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

Yes.

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.