What Is the Direction of Plane 1 Relative to Plane 2?

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The discussion revolves around determining the relative directions of two airplanes taxiing towards a terminal, specifically Plane 1 moving due north and Plane 2 moving at an angle north of west. Participants are exploring how to calculate the direction of one plane relative to the other.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the relative velocity and direction of Plane 1 with respect to Plane 2, using vector components and trigonometric functions. They express uncertainty in finding the direction of Plane 2 relative to Plane 1 and seek assistance. Other participants discuss the relationship between the two directions and suggest that the opposite direction can be found by adding or subtracting 180 degrees.

Discussion Status

Participants are actively engaging with the problem, with some providing confirmation of calculations while others express confusion about the direction of Plane 2 relative to Plane 1. There is a productive exchange of ideas, but no explicit consensus has been reached regarding the correct angle for Plane 2's direction.

Contextual Notes

Some participants mention difficulties with geometry and the interpretation of angles, indicating a potential gap in understanding the relationship between the two directional calculations.

bluefire90
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Two airplanes taxi as they approach the terminal. Plane 1 taxies with a speed of 11.3 m/s due north. Plane 2 taxies with a speed of 7.6 m/s in a direction 22.2° north of west. What is the direction of plane 1 relative to plane 2? Give the angle counterclockwise relative to the north. What is the direction of plane 2 relative to plane 1?

*I solved for magnitude first then velocity*

What is the magnitude of the velocity of plane 1 relative to plane 2?

To solve for the magnitude I found the vector components of plane 2:

Y component: 7.6 * sin(22.2°) = 2.87 m/s
X component: 7.6 * cos(22.2°)= 7.04 m/s
To find the final magnitude of the resultant vector I just used the pythagorean theorem after subtracting the plane 1 components FROM the plane 2 components.

2.87 m/s - 11.3 m/s = -8.43 m/s
7.04 m/s - 0 m/s = 7.04 m/s

Now to find the magnitude I used the pythagorean theorem.
Using the pythagorean theorom I got 10.98m/s as the relative velocity. This velocity is the same for plane 2 relative to plane 1.

To find the direction of plane 1 to plane 2 I just used the arctan formula

arctan (7.04/-8.43) = -39.86°
Now since its counterclockwise from north I just added to 360 to get 320° which is the correct answer.

I can't seem to figure out how to get the direction of plane 2 relative to plane 1 however and I've tried using the law of cosines and various other methods but I'm not sure where to go. Any help would be appreciated.
 
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Welcome to PF!

Hi bluefire90! Welcome to PF! :wink:
bluefire90 said:
I can't seem to figure out how to get the direction of plane 2 relative to plane 1 however and I've tried using the law of cosines and various other methods but I'm not sure where to go. Any help would be appreciated.

Yes, your results look fine.

And the direction of plane 2 relative to plane 1 is just the opposite of the direction of plane 1 relative to plane 2 (V21 = -V12).

So the opposite of 320º is … ? :smile:
 
Thanks for the help! Although I did try -320.0° and it wasn't correct! I thought the same thing though
 
bluefire90 said:
Thanks for the help! Although I did try -320.0° and it wasn't correct! I thought the same thing though

There's no such thing as -320º :rolleyes: … that would be 40º

but that isn't the opposite of 320º anyway, is it? :wink:

(just draw it! :smile:)
 
Haha my background in geometry is pretty weak but if I looked at it logically and drew it the opposite might be 130?
 
140 degrees i mean
 
Help! You're confusing me! :biggrin:

Yes, the opposite angle is always the original ± 180º. :smile:
 
haha thanks for the help! Wow that problem just made a lot more sense!
 

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