posted by Sandhya .
a) An infinite number of changes each equal to q are placed along the x-axis at x = 1, x = 2, x = 4, x = 8, . . . and so on. Find the potential and the esoteric at x = 0 due to this set of changes. What will be the potential and electric field if, in the above set-up, the corrective charges have opposite sign?
(b) Two metal spheres, each of mass 1 gm and radius 0.5 cm are placed on a smooth, horizontal, insulated plate such that their centres are 15 cm apart. One is charged to a potential 500 volt and the other to 1000 volt. What is the velocity of each sphere when they drift away to a distance of 30 cm. between their centres?
On the first, you will note a infinite series which should be recognized.
On the second I would start with total energy and set it equal to total energy (PE+KE) at 30cm.