Question

The work done in slowly moving an electron of charge e and mass m from a to b along a semicircular path in vertical plane in the field of charge q is

Answer 1

Work done = Force * displacement
W = - mg * 2r
W = -2mgr

Answer 2

The work done on an object caused by a force over a displacement can be calculated. The calculation involves only the force component along the displacement of the object.

The force component perpendicular to the displacement does zero work.

The change in kinetic energy of a particle is equal to the work done on it by the net force.

                                Work done = Force   x    displacement

                                Work done = - mg  x    2r  

                                Work done = -2mgr