How Fx = F(4/5) in this diagram?

[Benjamin_harsh]

Homework Statement

How Fx = F(4/5) in this diagram?

Relevant Equations

Fx = F(4/5)

$Fx = F\frac{4}{5}$

How Fx = F(4/5) in this diagram?

I am confused.

 

[lomidrevo]

Imagine that you are given an angle between the $\vec{F}$ and $\vec{F_y}$ instead of the small triangle in the diagram. How would you calculate the magnitude of $\vec{F_x}$?

Then, can you find a way how to get this angle from the small triangle shown in the diagram?

 

[Benjamin_harsh]

If I am not mistaken, I would say $\vec{F_x} = F_x.cos\theta$
Any one would be correct.

 

[ZapperZ]

If I am not mistaken, I would say $\vec{F_x} = F_x.sin\theta$ or $\vec{F_x} = F_x.cos\theta$
Any one would be correct.

You are mistaken.

First of all, you need to DEFINE where this "θ" is. There are at least 2 angles there, one made between F and Fx, the other between F and Fy.

If θ is the angle between F and Fx, then

F_x = |F|cos θ

BTW, it appears that you are having a lot of problem with math. This really isn't a physics question. This is not meant as a put-down, but rather to make you realize the source of your problems so that you may want to do something about it. Many of my students think that physics is tough, when what they are having problems with is not the physics, but the math. It seems that you are in the same situation.

Zz.

 

[lomidrevo]

If I am not mistaken, I would say
Any one would be correct.

I suggested the angle between $\vec{F}$ and $\vec{F_y}$ for a reason: I think it is easier to spot the same angle in the small triangle (just imagine that you can slide the triangle along the $\vec{F}$ toward the origin). But as already said, you can pick any of the angles, you just must stay consistent with your definition.
Also be careful "x" points vertically and "y" horizontally, that is a bit unconventional.