A window washer: tension problem

[DakE_FeatH]

Homework Statement

A window washer of mass M is sitting on a platform suspended by a system of cables and pulleys as shown. He is pulling on the cable with a force of magnitude F. The cables and pulleys are ideal (massless and frictionless), and the platform has negligible mass.

Homework Equations

F_net=ma
F_G=mg

3. The Attempt at a Solution [/b

I said the forces that are pulling the window washer up consist of a force equal to F and a force equal to the tension in the string attached to the platform.

Then, I took into calculation all the forces acting on the washer, which are the platform, the Earth and the cable.

I know that T is upward and F down, and T=|-F|

I need F

I am thinking F_net is F_N + T - F_G - F

And I am really stuck :(

 

[Redbelly98]

I think you can treat the person, platform, and bottom pulley as one object. Then you don't need to worry about the extra variable F_N, the normal force of the platform on the person.

So to get F_net, what are all the forces acting on the "object".

 

[DakE_FeatH]

All the forces acting on the object are T, F_G and F

so F_NET=T - F_G - F ?

or is it T=F_G+F
F = T - F_G ?

 

[Redbelly98]

F is upward. He pulls down on the rope, so it is pulling up on him (Newton's 3rd Law).

But we're not quite there yet. In how many different places does the rope pull upward on the object?