When will the work done be positive, negative and zero? State the criteria and also write two examples.

Hint: This question calls for the knowledge of the concept of work and its properties. Work is said to be done on an object, when force applied on the object causes the object to move. Work is a scalar quantity, it can be positive, negative or zero.

Complete answer:
Work is a physics term that describes the energy transfer that happens when an object is displaced over a distance by an external force that is applied in at least part of the displacement direction. Work can be calculated by multiplying the length of the path by the portion of the force acting along the path if the force is constant.

Positive work: The work done on an object is said to be positive work when the force and displacement are in the same direction. Example: A man pushing a car forward by applying force results in forward movement of car. In this case, the work is referred to as positive work.

Negative work: Negative work is done when the displacement is in the opposite direction of the applied force.For instance, on a rocket travelling perpendicularly upwards, work was done using gravity.

Zero work: When force and displacement are perpendicular to one another or when neither force nor displacement exists. When we move while having an object in our hands, the force acts in a downward direction, while displacement acts in a forward direction.

Note: There is no work, as described in this context, unless the object is displaced in some way and a part of the force is applied along the direction the object is moved. Since there is no displacement, holding a heavy object stationary does not shift energy to it.