how does the index of refraction of an unknown substance compare to the index of refraction of a vacuum? explain how the speed and the refraction of light would behave in both?

By measuring the speed of light in both in space and that unknown substance

Explanation:

Refractive Index (Index of Refraction) is a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density.

By measuring the speed of light in that medium and dividing it by speed of light 3*10^8 we can measure the refractive index of any medium

power out to power in less than 100%

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.