question_answer

No work is done by a force on an object if (a) The force is always perpendicular to its velocity (b) The force is always perpendicular to its acceleration (c) The object is stationary but the point of application of the force moves on the object (d) The object moves in such a way that the point of application of force remains fixed.

Answer:

(a), (b), (c)          (a) if\[\theta =\frac{\pi }{2},\,\,\cos \theta =O\,\,so\,\,W=O\] (b) force can never be\[\bot \]to its acceleration (c) for work to be done, object & point of application of force, both must move.