gravity and engine thrust engine thrust and friction friction and air resistance air resistance and gravity
I gave my students this multiple choice question: A jet plane is moving at a constant velocity on a flat surface. Which forces act against the forward motion of the plane?

Only one answer is correct among these 4 choices:
- gravity and engine thrust
- engine thrust and friction
- friction and air resistance
- air resistance and gravity

Could you tell me which one is correct?

friction and air resistance