Ablock falls from a ledge 10 m high. just before it hits the ground, its kinetic energy
a. equal to its potential energy at that point.
b. equal to zero.
c. increasing.
d. equal to its potential energy on the ledge.
e. all converted into thermal energy.
f. the same as on the ledge.

It would be D because the potential energy converts to kinetic energy on the way down. Hope it helped. :)

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.