Final answer:
The ground speed of the plane when there is a headwind of 70 m/s is 130 m/s, calculated by subtracting the headwind speed from the plane's airspeed.
Step-by-step explanation:
The ground speed of a plane relative to the ground in the presence of a headwind is calculated by subtracting the wind speed from the plane's airspeed. As indicated by the information provided, the plane flies north at 200 m/s while facing a headwind coming from the north at 70 m/s. Therefore, the resultant velocity or ground speed of the plane is:
200 m/s (plane's airspeed) - 70 m/s (headwind speed) = 130 m/s
Thus, the correct answer is C) 130.0 m/s, which represents the actual speed of the plane relative to the ground considering the effects of the headwind.