A window washer of inertia M is sitting on a platform suspended by a system of cables and pulleys as shown (Figure 1) . 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 inertia.

**Answer 1**

Assuming this is your figure:

https://www.flickr.com/photos/[email protected]/3305545…

then

if the rope tension is F, then the total force pulling down on the top pulley is 2F; therefore the total forces pulling down on the overhead support are

F + 2F = 3F.

These must sum to the weight of the window washer (and his accoutrements):

M*g = 3F

so

F = M*g / 3

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