Forces acting on pulley when lifting a submerged object in water
Answers
I have noticed that the other answers here deal with the 'actual' weight being loaded at the fixed point of the pulley, distributing force uniformly through the ropes etc.
However, this is not so.
The pulley commonly used to to lift buckets of water from a well is a Single fixed pulley.
Here the load (the weight of the bucket) is equal to the effort applied by you on the other end of the rope. So you need to apply the same force as the weight of the bucket.
This is also the case when no pulley is used at all, i.e. the effort required is the same in both cases!
How then does a pulley make it easier to lift the bucket?
The answer is that the pulley helps us apply the same force in a convenient direction i.e. in the direction of gravity-downwards. By doing so you can use your own weight in applying the effort( mind you the effort to be applied is still the the same).
So, here all you have to do is grasp the rope and throw your weight downward as opposed to using only the muscles of your arm to try and lift the bucket out of the well without a pulley.
Therefore the pulley makes it 'easier' for you to lift the bucket, by changing the direction in which force is applied to a more convenient one.