if gravitational potential energy is converted into mechanical kinetic energy explain why a dam's gravitational potential energy is always more than the mechanical kinetic energy it produces

Light traveling in water, nwater = 1.33, strikes a plastic block at an angle of incidence of 51.4°; part of the beam is reflected and part is refracted. if the index of refraction of the plastic is 2.0, what is the angle made by the reflected and refracted beams?