I am most obliged if someone can clear my
doubts on pulley system:

1. Why is a movable pulley more efficient than a fixed pulley?
2. What governs the efficiency of a movable pulley system?

Back to catalog.

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By movable I take it you mean a pully that turns on an axis.  A 
moveable pully is more efficient because the rope that  goes through
the pully does not have to slide over any surfaces.  Thus there is
little energy lost to `sliding' friction.  The less friction a pully
has the more efficient it is. If the axle of the pully is well 
lubricated it will be more efficient.