# Why is the center of mass of this system moving?

Here in this question , considering the system to be the thread , ladder and man , we can say that as the gravitational force which is and external force equal to 2Mg is acting in the downward direction and the pully exerts an equal and opposite force of 2Mg in the upward direction , hence the center of mass should not move as there is no external force to it as the tension in the thread and force applied by the man on the ladder and the normal force exerted by the ladder on the man as he moves up, are all internal force.

But in the solution the displacement of the center of mass is a non-zero quantity.

• Make a force diagram for the situation with the man climbing.
– nasu
Jun 9, 2022 at 9:45
• Jun 9, 2022 at 10:28
• @Steeven The ladder does not touch the floor. It is attached to the rope.
– nasu
Jun 9, 2022 at 13:58
• @nasu Yes i have drawn the force diagram but cannot still figure out what the external force to the system is.
– user327809
Jun 9, 2022 at 14:12
• Where is it? I cnnot see it.
– nasu
Jun 9, 2022 at 17:16