Light that enters the new medium <em>perpendicular to the surface</em> keeps sailing straight through the new medium unrefracted (in the same direction).
Perpendicular to the surface is the "normal" to the surface. So the angle of incidence (angle between the laser and the normal) is zero, and the law of refraction (just like the law of reflection) predicts an angle of zero between the normal and the refracted (or the reflected) beam.
Moral of the story: If you want your laser to keep going in the same direction after it enters the water, or to bounce back in the same direction it came from when it hits the mirror, then shoot it <em>straight on</em> to the surface, perpendicular to it.
Displacement will be 15 too because
It falls from 0 till 15 meters
The correct answers are: Options 2,4 and, 5
2)He solved Ptolemy’s model by proving elliptical orbits.
4)He determined that planets move faster when closer to the Sun.
5)He discovered laws of planetary motion.
