Show that a force that does no Work must be a velocity-dependent force.
To prove that a force with doing no works must be a velocity-dependent force, it is necessary to assume that zero work is done by the force. As given in the following equation:
We can write
So, it is proven that the force F is dependent on the velocity, it implies there is a 90° angle between F and v. So if the velocity changes its direction, simultaneously the direction of the force will also change.