Football helmets are made with padding that reduce head injuries when a player collides with an object. which best explains how the padding reduces injuries? a) it extends the time of the collision b)  it reduces the time of the collision  c) it eliminates the reaction force of the object d) it eliminates the action force of the object.

In padding helmets we have pads or cushions on it which will move inwards when ball hits the helmets

Now due to this the collision time will increase and ball is not immediately rebound with the helmets

so as we know the Newton's law

so here if collision time is increased then we will have less force

so the impact of collision will be less

So the correct answer will be

A) It extends the time of the collision

On the application of padding, the time of the collision (or the reaction time) increases. Hence, option (A) is correct.

The average force acting on any object for a very small interval of time is called Impulse. As per the impulse-momentum theorem, "The product of average force and time interval is equal to the change in momentum.

The mathematical expression for the impulse-momentum theorem is,

Here,

 is the change in momentum.

t is the time interval or the reaction time.

F is the average force.

Clearly, the average force is inversely proportional to the reaction time. Due to padding, the reaction time increases, and the magnitude of average force decreases. This reduces head injury.

Thus, we can conclude that on the application of padding, the time of the collision (or the reaction time) increases. Hence, option (A) is correct.

Learn more about the Impulse-Momentum Theorem here:

link

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.