Question

derivation for WORK DONE BY A CONSTANT FORCE.​

Answer 1

Work is done when a force is applied, at least partially, in the direction of the displacement of the object. If that force is constant then the work done by the force is the dot product of the force with the displacement

W=  F ∙  d

The net work done on an object (the work of the net force) is equal to the energy added to the object. This is the reason for both the unit of work being the Joule, \text{J}J, and the work-kinetic energy theorem:  

W=ΔK.