A pebble of mass 50g is moving with a velocity of 20m/s. What is its kinetic energy?

We know that, to find the Kinetic energy we are required mass and velocity and Here Both parameters are provided But mass is in gram so we need change it into kg,

1g = 0.001kg,

⠀⠀⠀50g = 0.05g

Now we know the formula of Kinetic energy,

Hence, the kinetic energy of the pebble is 10J.

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.