CBSE Class 9 Answered
HI dear.
I should appreciate your interest and inquisitiveness to learn things.
The work is zero only if the force is a conservative one. A conservative force is a force with preperty that the work done in moving a particle between two points is independent of the path taken. If particle travels in a closed loop , as you say, a square or circular path, the net work done by a conservative force is zero.
But, there are non-conservative forces the forces that do not store energy....For example, you push a book,but, where is the kinetic energy now?
Friction is a non conservative force.
Work done = change in potential energy + change in kinetic energy..
Hope this is okay..
Regards,
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