In the design of a rapid transit system, it is necessary to balance the average speed of a train against the distance between stops. the more stops there are, the slower the train's average speed. to get an idea of this problem, calculate the time it takes a train to make a 9.0 km trip in two situations. (assume that at each station the train accelerates at a rate of 1.1 m/s2 until it reaches 95 km/h , then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at -2.0 m/s2 . assume it stops at each intermediate station for 27.0 s .)

because growing process had stoped after 4-5 year

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.