Question

When do we say the work is done?

Answer 1

Hint: For work to be done by one body on another, the body must apply a non-zero force on the other body, the displacement of the body on which force is applied should not be zero, and the displacement of the body should not be at right angle to force.

Complete Step By Step Solution:
Work is integral to force with respect to small change in displacement. In physics, the terms work and energy have the same meaning. When a body does positive work on another body, it means that the body transmits the same amount of energy to the other body.
Mathematically we can write
$W=\int{Fds}\cos \theta$ ,
where $\theta$ is the angle between force and displacement.
In physics for work to be done we have three conditions
The force applied by the body, which wants to do work, should not be zero.
The displacement of the body on which the work is done should not be zero.
The angle between displacement (of the body on which the work is done) and force applied by the body (which wants to do work) should not be ${{90}^{\circ }}$.

If all the above conditions are fulfilled then we can the body has done work or some work is done.

Note: If the work done by the body is positive, this means that the body has transferred energy to another body (the one on which the work is done). If the work done by the body is negative, this means that the body has gained energy from another body (the one which has done work).