An object is acted upon by a constant force which gives it a constant acceleration a. at a certain time t1, having started from rest at t = 0, it has kinetic energy k1. at what time t2 has its kinetic energy doubled?

Explanation:

The kinetic energy of a body is that energy it possesses due to its motion. In classical mechanics, this energy depends only on its mass and speed, as follows:

The speed in an uniformly accelerated motion is given by:

Replacing this expression in the formula for the kinetic energy, we have:

So, if we have :

Equaling (1) and (2) and solving for :

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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.