Vectors in the direction of axis

dbone_7

I have been having a debate that a vector in the positive x-direction must not have a y component other than 0. What are the other opinions on this wording and other possible wordings to mean that a vector is on the same line as an axis?

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neurocomp2003

umm you waited 10 minutes on an open forum? perhaps you should reword what you are asking.

"what words to mean that a vector is on the same line as an axis"...hmm how about none ...lets use variables (x,y,z) thats for any axis...now by your wording i'd assume you meant a standard axis like x-axis,y-axis,z-axis or ei,ej,ek. So (a,0,0) and (0,b,0) and (0,0,c) where a,b,c!=0 all lie on their respective standard axis.
now you also asked about "positive x-direction vector" ...any vector with the x-component >0 is considered such a vector regardless of the other 2 components. with the other 2 components=0 you get a standard axis vector. x-axis,y-axis,z-axis or ei,ej,ek.

dbone_7

I have been having a debate that a vector in the positive x direction must not have a y component other than 0. Is that view correct or do all vectors with a positive x component "point in the positive x direction"? What are the other opinions on this wording and other possible wordings to mean that a vector is on the same line as an axis? My professor uses the meaning with the idea that a vector in the positive x direction points in the same direction as the positive x axis so it is similar to saying a vector in the positive x axis direction.

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dbone_7

I'll rephrase it slightly,

I have been having a debate that a vector in the positive x direction must not have a y component other than 0. Is that view correct or do all vectors with a positive x component "point in the positive x direction"? What are the other opinions on this wording and other possible wordings to mean that a vector is on the same line as an axis? My professor uses the meaning with the idea that a vector in the positive x direction points in the same direction as the positive x axis so it is similar to saying a vector in the positive x axis direction.

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FUNKER

although it is vague, it is reasonable to assume that when a vector is in the positive x direction it only has a component in the x axis. I see no need to be pedantic about it.

Tide

Homework Helper
If a vector has a y component then it is not pointing in the x direction. Also, a vector pointing in the x direction is parallel to the x axis.

Tide

Homework Helper
You should only post your question in one area. Your other posting has already been answered.

rcgldr

Homework Helper
This is more of a language / logic issue:

The statement "a vector in the positive x axis" implies the vector has no other component.

A "vector with a component in the x axis" implies that the vector may or may not have a component along one or more other axis.

ZapperZ

Staff Emeritus
2018 Award
This thread has been merged, but I haven't pruned the postings. So things may appear out of place.

Please DO NOT do multiple post (read our Guidelines if you have forgotten).

Zz.

FocusedWolf

Hi everyone, i'm having trouble calculating a vector direction that my schools online homework thing will accept, and i don't know why and i'm going nuts cause this stuff is easy!

Consider four vectors ~F1, ~F2, ~F3, and ~F4,
where their magnitudes are
F1 = 48 N,
F2 = 22 N,
F3 = 24 N, and
F4 = 50 N.

Let
theta1 = 150 degrees,
theta2 = -140 degrees,
theta3 = 20 degrees, and
theta4 = -63 degrees, measured from the positive x axis
with the counter-clockwise angular direction
as positive.

What is the magnitude of the resultant vec-
tor ~F , where ~F = ~F1 + ~F2 + ~F3 + ~F4? Answer
in units of N.
My work found the resultant vector to be:

-13.17 i - 26.48 j , with a magnitude of 29.5772

This online homework thing accepted my magnitude as the correct answer for this problem, which means my vector addition was ok. My problem is in finding whats wrong with how i determine the direction for the next problem that uses the answer from this one.

(part 2 of 2)
What is the direction of this resultant vector
~F?

Note: Give the angle in degrees, use coun-
terclockwise as the positive angular direction,
between the limits of -180 degrees and +180 degrees from
the positive x axis. Answer in units of degrees.
Can someone explain to me that "Note:"?

my answer for this was 116.441 degrees when i tried one way, (solving for theta when i subbed the x component of the vector and the magnitude into x = R cos(theta) as x = Magnitude*cos(theta)). I also tried adding 180 to that answer in case that crazy note meant to do that, and i tried the arctan(y component / x component) = 63.56 degrees, which the site also said was wrong answer. I am really confussed on this.

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