Ahockey puck is set in motion across a frozen pond. if ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is a) zero. b) equal to its weight divided by its mass. c) equal to the product of its mass times its weight.

Zero

Explanation:

According to Newton's second law, the net force acting on an object is equal to the product between the object's mass and its acceleration:

F = ma

For the hockey puck, there are no forces acting on it during its motion, since ice friction and air resistance are negligible. This means that the net force is zero:

F = 0

But this means that the acceleration is also zero:

a = 0

So the hockey puck is moving already at constant velocity. Therefore, there is no need for additional forces.

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.