You get into an elevator and step onto a bathroom scale, which shows you weigh 150 pounds. The doors close, and the elevator starts to move, very smoothly. You look down, and notice that your weight is now 155 pounds. What can you say about the motion of the elevator? (A) It is moving upward, but slowing down.
(B) It is moving downward, and speeding up.
(C) It is moving downward, but slowing down.
(D) It is moving upward, at a constant speed.

A

Explanation:

the total distance traveled by the car is

30km + 49km = 79 km .

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.