Understanding the Situation
* Plane's Speed: 80 mi/hr (relative to the air)
* Headwind: 10 mi/hr (acting against the plane's motion)
Calculating Resultant Velocity
A headwind reduces the plane's ground speed. To find the resultant velocity, simply subtract the headwind speed from the plane's airspeed:
Resultant Velocity = Plane's Speed - Headwind Speed
Resultant Velocity = 80 mi/hr - 10 mi/hr
Resultant Velocity = 70 mi/hr
Therefore, the magnitude of the plane's resultant velocity is 70 mi/hr.
