An airplane is flying on a compass heading(bearing) of 340 degrees art 325 mph. A wind is blowing with the bearing 320 degrees at 40 mph, how do you find the component form of the velocity of the airplane?

1 Answer
Jun 6, 2016

Below are the formulas for X- and Y-components of the resulting movement as well as the amplitude and angle of this movement (all angles are measured according to trigonometric standard).

Explanation:

In navigation the angle of the course (on a compass) is counted clockwise from the North (so, the direction to the North is 0o, to the East is 900, to the South is 180o and to the West is 270o).
The North on most maps is a vertically up direction.
In coordinate Geometry and Trigonometry, which we will use, angles are measured counterclockwise from the positive direction of the horizontal X-axis (the East on most maps).

Let's make a simple transformation into Trigonometric standard using the direction to the East as an X-axis.:
340o on a compass is 90o+(360o340o)=110o counterclockwise from the X-axis.
320o on a compass is 90o+(360o320o)=130o counterclockwise from the X-axis.

This is a problem on addition of two vectors. Each is defined by its amplitude and angle of direction:
airplane (vector A) has amplitude 325 (mph) and angle 110o;
wind (vector W) has amplitude 40 (mph) and angle 130o.

To add these two vectors, we represent both as sums of X-component and Y-component:
AX=345cos(110o)
AY=345sin(110o)
WX=40cos(130o)
WY=40sin(1300)

Both X-components act along the same direction, both Y-components act along the same direction. So, we can add X-components to get an X-component of the resulting movement and add Y-components to get a Y-component of the resulting movement.

(A+W)X=AX+WX=345cos(110o)+40cos(130o)
(A+W)Y=AY+WY=345sin(110o)+40sin(130o)

Knowing two components of the resulting vector of movement, we can easily determine the amplitude |A+W| and direction (A+W) of the resulting vector:

|A+W|=(A+W)2X+(A+W)2Y

(A+W)=arctan[(A+W)Y(A+W)X]

We leave the calculations to the person who suggested the problem.

If it's necessary to express the angle (A+W) in compass format (α) from its standard trigonometric format (β), use the conversion formula
α=360o(β90o)=450oβ
(if the result is greater than 360o, subtract 360o)