1. A 40 kg rock falls from rest from the top of a 64 m high tower and falls with negligible air resistance. How much kinetic energy (KE) and potential energy (PE) does the rock have when it is 28 m above the ground?
(A) KE = 0; PE = 2.5 x 104

J (B) KE = 1.1 x 104 J; PE = 1.4 x 104

J (C) KE = 1.4 x 104 J; PE = 1.1 x 104

J (D) KE = 2.5 x 104 J; PE = 0

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.