TABLE OF CONTENTS Definition. A force is said to do work when its points of application undergo a displacement.
If the force is constant in magnitude and direction, then the amount of work done is measured by the product of the force and the displacement in the direction of the force.
( a) When the displacement of the body is in the direction of the force.
Suppose a body is acted upon by a number of forces. Let the point of application of a force F be moved from O to A where OA = s.
If the displacement takes place in the direction of the line of action of the force [as in Fig. (a)] then work done = F. s and is positive as the displacement is in the direction of the force.
If the displacement is in the same line as the line of action of the force but in opposite direction [as in Fig. (b)], then work done is negative.
Work done in this case = F. s.
In this case, there must be other forces acting on the body, otherwise, a single force F cannot move the body in a direction opposite to its own.
( b) When the displacement of the body is in a direction oblique to the direction of the force.
Let the point of application O be displaced to A such that OA makes...
