Work done by force applied for an instant We know ${\rm work} = \int F \cdot dl$ , where $dl$ is the displacement of point of application of force.
Suppose I apply an instant force of $100~\rm N$ on a body and then remove the force; after that the body moves a distance $d$. When the body is moving there is no external force (other than friction, $mg$, normal reaction force). So what is the work done by $100~\rm N$ force?
Is is zero? Because when the body moved distance $d$, the $100~\rm N$ force was not there.
 A: $d=0$ in your example, because the work is zero and so the kinetic energy of the body is zero. A finite force applied for an instant doesn't do any work.
A: The work done by the force would be F*d, where d is the distance it travels WHILE the force is still being applied. The work done by the force provides the block some kinetic energy, i.e its velocity. Since the block is coming to a halt, friction or other drag forces must be acting on the body. The work done by these drag forces dissipates the kinetic energy of the block in form oh heat/sound and bring it to a halt.
A: Work done =  Force being applied on the body * displacement is travels while is the force is still present on the body.
Therefore , Force applied when removed after certain moment becomes 0 on the body. We won’t consider the displacement it travels because that is not the distance it travelled while the force was present on the body.
Therefore , W = 0 but we can also say that work done would be wrong to calculate for such a moment which can be said as not defined.
