A physics teacher is on the west side of a lake and wants to swim across and end up at a point directly across from his starting point. He notices that there is a current in the lake and that a leaf floating by him travels 4.2 m [S] in 5.0 s. He is able to swim 1.9 m/s in calm water. a) Using a vector diagram, what direction will he have to swim in order to arrive at a point directly across from his position?

b) Calculate his velocity relative to the shore.

c) If the lake is 1.1 km wide, how long, in seconds, will it take him to cross?

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.

the answer to this is proletariats.

hope this : )