# Window washer

1. Jul 11, 2009

### clarineterr

1. The problem statement, all variables and given/known data
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.Find the magnitude of the minimum force F that allows the window washer to move upward.
Express your answer in terms of the mass M and the magnitude of the acceleration due to gravity g.

2. Relevant equations

Newton's second Law

3. The attempt at a solution

For the person: Ma = F + T -Mg where T is the tension in the cable holding the platform and F is the force of the rope on the washer.

Then from the lower washer T = 2T$$_{1}$$, where T$$_{1}$$ is the tension in the rope

So Ma = F + 2T$$_{1}$$ - Mg

The block is about to move so Ma = 0 and I think T$$_{1}$$=F so then

0 = 3F - Mg