10. What is the acceleration due to gravity on Planet X, if an object has a mass of 20 kg, weighs 74 Newtons?

Force = Mass * Acceleration,

Your force is 74 Newtons because force is measured in newtons, your mass is 20kg,

Plug it into the formula

74N= 20KG* ?M/S^2

Divide both sides by 20 to Isolate the Variable,

Your Acceleration would be 3.7 M/s^2

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.