A horizontal force of magnitude 45.6 N pushes a block of mass 4.28 kg across a floor where the coefficient of kinetic friction is 0.620. (a) How much work is done by that applied force on the block-floor system when the block slides through a displacement of 2.98 m across the floor?
(b) During that displacement, the thermal energy of the block increases by 40.0J. What is the increase in thermal energy of the floor?
(c) What is the increase in the kinetic energy of the block?

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.

yeah the answer is mean