While you're in a bus that moves at 100 km/h, you walk from the back to the front at 10 km/h. what is your speed relative to the road outside?
a) 90 km/h
b) 110 km/h
c) 100 km/h
d) 10 km/h

(B) 110 km/h

Explanation:

Since you are moving in the same direction as the bus and you are on the bus, your speed relative to the road will be the addition of the speed of the bus and the speed you are walking at.

Therefore your speed relative to the bus outside = 100 + 10 = 110 km/h

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.