$(a)$ Define work done by a constant force on an object. Write an expression for the work done.
$(b)$ How much work will be done on an object by a force if the displacement of the object is zero?
$(c)$ What is the kinetic energy of an object? Write an expression for the kinetic energy of an object of mass $m$ moving with a speed $v$.

(A) Work done by a force acting on an object is defined as the product of the magnitude of the force and the displacement of the object in the direction of the force.
The expression for work done is: $W = F \times s$,where $W$ is work,$F$ is force,and $s$ is displacement.
$(b)$ If the displacement of the object is zero,the work done is zero. This is because $W = F \times 0 = 0$.
$(c)$ Kinetic energy is the energy possessed by an object by virtue of its motion. The expression for the kinetic energy $(K)$ of an object of mass $m$ moving with a speed $v$ is $K = \frac{1}{2}mv^2$.