Question 9
In the third case of activity 2 (A: 6 N, B: 6 N) the trolley does not move. What does that mean?
The right answer is the one marked above.
Two equal forces act on the trolley in opposite directions and cancel each other. The resultant is zero, but the forces are there.
A zero resultant is not the absence of force. The trolley also stayed still in the first case (4 N and 4 N) — but the pull on the threads is greater in the third. Keep increasing it and the thread will snap.