The water in the river moves with the speed 0.523 km/h. Alice and Bob can swim with the speed 2.62 km/h with respect to the water. They want to get from point A on one bank of the river to point B directly across on the other bank. Alice swims along the straight line AB, while Bob swims with a velocity perpendicular to the river and lets the flow take him some distance downstream. After that, he walks to point B along the river. What is the speed of his walk if he reaches point B at the same time as Alice

grav force prop 1/r squared 2r all squared is 4rsquared 1/4rsquared quartered

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.

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