Question 9
What is the line of action of a force?
The right answer is the one marked above.
The straight line drawn from the point, showing the direction the force acts in. The direction in which a force acts at a point can be shown by a straight line drawn from that point.
It is an idea about the force's direction, not its magnitude. The magnitude is given separately, in newtons.
Do not confuse it with the path the object travels. A force can be applied without the object moving at all — and it still has a line of action.