Question 5
What does it mean to speak of the resultant of three forces applied in the same direction?
The right answer is the one marked above.
One force acts that could be put in place of the original three. Had there been one person applying that much force instead of three, the car would have moved in exactly the same way.
It is not a fourth force — nothing new is added. Nor does only the largest act; all of them act, but their combined effect can be described by one.