The common way of finding the work done on some object is by applying the equation: force*displacement.

However, suppose we apply a force of F newtons on an object of mass M for a duration of T seconds. We can then express the work done in terms of T and F, by expressing the change in velocity in terms F and T and then by applying the work-energy theorem. 

If we do some further substitutions (Express displacement in terms of F, initial velocity and T), we can show that the above 2 methods produce the same result for a given force (according to what I calculated, do correct me if I am wrong).

Why is the equation force*displacement used instead of the latter case? To me, calculating the work done with respect to time is more intuitive because the increase in momentum of an object (under a constant force) is the same per unit of time. On the other hand, the increase in momentum per unit of displacement of an object gets progressively smaller due to the acceleration of the object.