Low velocity im pretty sure
Answer:
It can occur only when light is incident on an interface where the index of refraction on the other side is less.
Explanation:
When the light passes from a denser medium, with refractive index n1, to another less dense medium, with refractive index n2, the incident light beam is refracted in such a way that it is not able to cross the surface between both media, the light beam is fully reflected and completely confining in the optically denser medium through which it propagates. For this phenomenon to occur, it is necessary that the angle of the incident light beam with respect to the normal be greater than or equal to the critical incidence angle θc. The critical angle can be calculated as :

Answer:
The work done to lift the counterweight equals the potential energy acquired
Explanation:
since this is vertically applied force on the counterweight, and the distance the force is displacing the counterweight is in the same direction as the applied force, it equals the gained potential energy
It takes work to push charge through a change of potential.
There's no change of potential along an equipotential path,
so that path doesn't require any work.