Consider an object with no net force acting on it moving with a constant velocity $v$. It has a momentum $mv$.
Now let a force $F_1$ act on the object. Let the direction of this force be opposite (to the direction of the object's constant velocity)
The object now undergoes a change in its momentum over time, accelerating in the direction of the force $F_1$
Let another force $F_2$ be introduced that is equal in magnitude to $F_1$ but opposite in direction.
Question: What happens to the object now?
Since under the influenced of balanced forces the object can either be at rest or have a constant velocity. If it does have a constant velocity what will be its direction?
And what is the work done by the two forces?