Explain work done by a constant force.

(N/A) Constant force: When the magnitude and direction of a force acting on a body remain constant during its motion,such a force is known as a constant force.
Work: The work done by a constant force is defined as the dot product of the force vector $\vec{F}$ and the displacement vector $\vec{d}$.
$\therefore W = \vec{F} \cdot \vec{d} = F d \cos \theta$
where $F$ is the magnitude of the force,$d$ is the magnitude of displacement,and $\theta$ is the angle between the force vector and the displacement vector.
If the displacement is not in the direction of the applied force,work can be calculated in two ways:
$(1)$ Work $=$ (Force) $\times$ (Component of displacement in the direction of force) $= F(d \cos \theta)$
$(2)$ Work $=$ (Component of force in the direction of displacement) $\times$ (Displacement) $= (F \cos \theta)d$
As shown in the figure,when a force $\vec{F}$ acts at an angle $\theta$ to the displacement $\vec{d}$:
$(i)$ The component of force in the direction of displacement is $F \cos \theta$,which is responsible for the work done.
$(ii)$ The perpendicular component $F \sin \theta$ does no work because it is perpendicular to the displacement.