# Homework Help: Relative Velocity

1. Oct 26, 2009

### waldvocm

An airplane is heading due west. The airplane's speed relative to the air is 150.0 km/h. If there is a wind of 24.4km/h toward the north, what is a) the magnitude (km/h)

I used the equation sqrt 150.0^2+24.4^2 =151.97

b)what is the direction (degrees measured from west) of the velocity of the plane relative to the ground?

tan-1(24.4/150.0)=9.23 Would you add 90degrees to this =99.23

2. Oct 26, 2009

### Seannation

Well since the wind is north and the plane is heading due west, it must be within 270 and 360 degrees (on a compass).

3. Oct 26, 2009

### waldvocm

I dont understand that.

Since it is heading due west, which would be on the -x axis. And the wind is blowing north wouldn't the angle be in the 2nd quadrant relative to the ground. Which would place the vector in the second quadrant between 90 and 180 degrees?

Can you elaborate on your previous response?

4. Oct 26, 2009

### willem2

The question asks for "degrees measured from west". I would answet it as "9.23 degrees north of west"

Compass courses differ from the angles that are used in mathematics N 0, E 90, S 180, W 270.