Question

Give two examples of (i) positive work, (ii) negative work, (iii) zero work.

Answer 1

Hint: If force and displacement would be in the same way, it is stated that the work carried out on an object is positive, and if they are in opposite ways, it is negative work done. If force and displacement become perpendicular to one another, it is zero work.

Stepwise solution:

(i) Example of positive work:
a. If we take the top sheet off the table when the dishes are already sitting on it, as a result of the friction forces of the cover, the dishes will continue to roll. The work done on the dishes through tension would be positive.
b. If we kick a football, then the football will travel along the direction of force applied. Therefore work done on the football will be positive.

(ii) Example of negative work:
a. When we push a book to just a distance, the work performed by the frictional force will be negative.
b. The work that the buoyant force does when a coin sinks.

(iii) Example of zero work:
a. Zero work is done if a block is travelling on a flat horizontal surface.
b. For hours, you rest on a chair. Zero work is done as motion is not involved.


Note:

In physics, work is the method of converting energy by the application due to force to the motion of a body, often expressed as the result of force and displacement. When the force has a portion in the direction of displacement of a point of application, a force is shown to do positive work.