When an airplane flies, its total velocity with respect to the ground is :

V total = v plane + v wind

Where v plane denotes the plane velocity through

motionless air, and v wind denotes the wind's velocity crucially, all the quantities in this equation are vectors. The magnitude of a velocity vector is often called the "speed".

Consider an airplane whose speed through motionless air is 100 m/s. To reach its destination, the plane must fly east.

The "heading" of a plane is the direction in which the nose of the plane points. So, it is the direction in which the engines propel the plane.

(i) If the plane has a eastward heading, and a 20 m/s wind blows towards the southwest, then the plane's speed is –