# Determining the forces acting on a system

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1. Oct 19, 2015

### Mr Davis 97

1. The problem statement, all variables and given/known data
Explain why the force diagram is as shown:

http://[ATTACH=full]199944[/ATTACH]

[B]2. Relevant equations[/B]

[B]3. The attempt at a solution
[/B]
For the system, the gravity vector makes sense. However, I don not understand exactly why there are three tension forces. First of all, to me, it would seem that the first force is the force due to friction between the person's hands and the rope. I do not see what the force has to do with tension. Second of all, why are there two tension forces where the bottom pulley is? Shouldn't there only be one? How come there are two? I doon't really understand how tension works, so it is confusing me.

Last edited by a moderator: May 7, 2017
2. Oct 19, 2015

### davidmoore63@y

The hands versus the rope: think Newton's third law.

For the second question, consider that the tension along a rope must the the same (assuming the pulleys are frictionless), otherwise it would move