Question

A steel ball of weight 50 N hangs at a height of 5.0 m above the ground, on the end of a chain 2.0m in length. How much work is done on the ball by gravity, and by the tension in the chair?
Draw the diagram, if possible.

Answer 1

0 displacement so 0 work done by all the forces like gravity , tension

W = F.s = F x 0 cosa = 0

Answer 2

Work is done by a Force (gravity of Earth here) when the object is displaced by the force.

case 1: This is trivial case of no work done.
       Here if the ball is stationary, then there is no work done in holding the ball at  the same position of 5 meters above ground.
      then work = 0 Joules

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Case 2.   I suppose you are not looking for a trivial answer.

If you want to know the work done by gravity in lifting the ball from ground level to the height of 5m, then it is not zero.
 
Work done in lifting the ball up by 5 m from ground 
   =  Force * Displacement 
   =  Weight * (- height)
   = - m g h
   = - 50 N * 5 m
   = - 250 Joules.

Force and displacement are in different directions. Hence it is negative. As work done is negative, the total energy of the ball increases by that amount.

This work done will be different if the ball was lifted from another height.