NATURE OF WORK
¶¶ POSITIVE WORK:
Workdone is said to be positive if applied force or one of it’s components is in the direction of displacement.
therefore W=FScos0°=positive.
If the force is in the same direction as the displacement, then the angle is 0 degrees
EXAMPLES:
1.Workdone by the gravitational force on a freely falling body is positive.
2.When a spring is stretched ,both the stretching force and displacement act in the same direction so workdone is positive.
3.When a block is lifted from the ground the workdone by lifting force is positive.
4.When a horse pulls a cart the applied force and displacement are in the same direction so work done by horse is positive.
¶¶ NEGATIVE WORK:
Workdone by a force is said to be negative if the applied force has a component in a direction opposite to that of the displacement.
EXAMPLES:
1.When a body is dragged on rough surface,workdone by frictional force is negative.
2.Workdone by the gravitational force on a vertically projected up body is negative.
¶¶ ZERO WORK:
If a body displaces perpendicular to the direction of force then the workdone is zero.
If there is no displacement then workdone is zero.
EXAMPLES:
1.A person carriyng a load and moving horizontally on a platform does no work against gravity.
2.When abody moves in a circle the workdone by the centripetal force is zero.
3.The tension in the string of a simple pendulum is always perpendicular to it’s displacement so,workdone by tension is zero.
4.A person carrying a load on his head and standing at a given place is zero.