Finding Polar Coordinates for Vector B⃗ = -2.0ι^ + 3.0 j^

In summary, the polar coordinates for vector B are r = 3.6 and θ = 124 degrees. It is important to plot the original cartesian coordinates to accurately determine the correct quadrant and angle for the polar coordinates.
  • #1
Flinze
23
1

Homework Statement


B⃗ = -2.0ι^ + 3.0 j^.
Find the polar coordinates r and theta.

Homework Equations


n/a

The Attempt at a Solution


r=sqrt((-2.0)^2+(3.0^2))
r = 3.6

theta = tan^-1(3/-2) = -56 degrees

The answers seem to be wrong, can I get any guidance on this question please?
 
Physics news on Phys.org
  • #2
Draw a picture. Where is the Cartesian point? Why doesn't your angle make any sense?
 
  • Like
Likes Flinze
  • #3
brainpushups said:
Draw a picture. Where is the Cartesian point? Why doesn't your angle make any sense?

Oh it's in the second quadrant, I see how the angle wouldn't work. So would it then be +56 degrees?
 
  • #4
Flinze said:
Oh it's in the second quadrant, I see how the angle wouldn't work. So would it then be +56 degrees?
Is that in the correct quadrant?
Do you know what the graph of tan looks like? If you put a horizontal line through it at a random height, what can you say about the intercepts?
 
  • Like
Likes Flinze
  • #5
haruspex said:
Is that in the correct quadrant?
Do you know what the graph of tan looks like? If you put a horizontal line through it at a random height, what can you say about the intercepts?
I believe it is on the correct quadrant as -x,+y = quadrant 2. And there should only be one intercept I believe?? I'm confused
 
  • #6
Flinze said:
Oh it's in the second quadrant, I see how the angle wouldn't work. So would it then be +56 degrees?
Which quadrants have positive angles?
Where is zero degrees located?
How many degrees in each quadrant?
 
  • Like
Likes Flinze
  • #7
SteamKing said:
Which quadrants have positive angles?
Where is zero degrees located?
How many degrees in each quadrant?
Quadrant I, and III have positive angles I believe There are 90 degrees in each quadrant, and zero is located on the x-axis on quadrant I.
 
  • #8
Flinze said:
Quadrant I, and III have positive angles I believe There are 90 degrees in each quadrant, and zero is located on the x-axis on quadrant I.
Well 2 out of 3 isn't bad, but it should be three out of three in this case.

If you start at zero degrees and go counterclockwise to 180 degrees, which quadrants have positive angles?

If you start at zero degrees and go clockwise to 180 degrees, which quadrants have negative angles?

The tricky thing about arctan on your calculator is it returns an angle θ such that -π/2 ≤ θ ≤ π/2, and the user is left with deciding in which quadrant the proper angle falls and its measure from zero degrees. That's why you should plot the original cartesian coordinates.
 
  • Like
Likes Flinze
  • #9
Flinze said:
I believe it is on the correct quadrant as -x,+y = quadrant 2. And there should only be one intercept I believe?? I'm confused
Sure, but +56 degrees is not in that quadrant.
For the intercepts, what range of angles did you consider in saying there is only one intercept?
 
  • Like
Likes Flinze
  • #10
SteamKing said:
Well 2 out of 3 isn't bad, but it should be three out of three in this case.

If you start at zero degrees and go counterclockwise to 180 degrees, which quadrants have positive angles?

If you start at zero degrees and go clockwise to 180 degrees, which quadrants have negative angles?

The tricky thing about arctan on your calculator is it returns an angle θ such that -π/2 ≤ θ ≤ π/2, and the user is left with deciding in which quadrant the proper angle falls and its measure from zero degrees. That's why you should plot the original cartesian coordinates.

Quadrant I would be positive for the first part, and Quadrant IV would be negative on the second question.
So then what I would do is 180-54=124?
 
  • #11
haruspex said:
Sure, but +56 degrees is not in that quadrant.
For the intercepts, what range of angles did you consider in saying there is only one intercept?
The answer -56 would be in quadrant IV and +56 would be in quadrant one then right?
 
  • #12
Flinze said:
The answer -56 would be in quadrant IV and +56 would be in quadrant one then right?
You're still guessing here. I don't know why you won't plot the original cartesian coordinates. That would answer your question directly.
 
  • Like
Likes Flinze
  • #13
SteamKing said:
You're still guessing here. I don't know why you won't plot the original cartesian coordinates. That would answer your question directly.
It would be in quadrant II after I plot (-2,3). Would the angle I be measuring start from the x-axis from quadrant I though?
 
  • #14
Flinze said:
It would be in quadrant II after I plot (-2,3). Would the angle I be measuring start from the x-axis from quadrant I though?
Never mind, I figured it out, I subtracted 180 with 56 = 124 degrees. Thanks.
 

Related to Finding Polar Coordinates for Vector B⃗ = -2.0ι^ + 3.0 j^

1. What are polar coordinates?

Polar coordinates are a way of representing a point in a two-dimensional coordinate system using a distance from the origin (known as the radius) and an angle from a reference direction (usually the positive x-axis).

2. How do you calculate polar coordinates?

To calculate polar coordinates, you first need to identify the radius and the angle for the point you are trying to represent. Then, you can use the formula r = √(x² + y²) to find the radius, and the formula θ = tan⁻¹(y/x) to find the angle.

3. How are polar coordinates different from Cartesian coordinates?

Polar coordinates use distance and angle to represent a point, while Cartesian coordinates use x and y coordinates. Polar coordinates are better suited for representing circular and symmetrical shapes, while Cartesian coordinates are better for representing straight lines.

4. How do you convert polar coordinates to Cartesian coordinates?

To convert polar coordinates to Cartesian coordinates, you can use the formulas x = r cos(θ) and y = r sin(θ), where r is the radius and θ is the angle. This will give you the x and y coordinates for the point in the Cartesian coordinate system.

5. What is the purpose of using polar coordinates?

Polar coordinates are often used in situations where a point has a circular or symmetrical pattern, as it can be easier to describe a point using a distance and angle rather than x and y coordinates. They are also useful in physics and engineering for representing forces and motion in a circular motion.

Similar threads

  • Introductory Physics Homework Help
Replies
10
Views
280
  • Introductory Physics Homework Help
Replies
13
Views
529
  • Introductory Physics Homework Help
Replies
1
Views
915
  • Introductory Physics Homework Help
Replies
8
Views
12K
  • Introductory Physics Homework Help
Replies
12
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
979
  • Introductory Physics Homework Help
Replies
4
Views
955
  • Introductory Physics Homework Help
2
Replies
37
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
961
  • Introductory Physics Homework Help
Replies
9
Views
2K
Back
Top