Police investigators examining the scene of an accident involving two cars measure 79-meter long skidmarks of one of the cars which nearly came to a stop before colliding. the coefficient of kinetic friction between rubber and the pavement is about 0.82. estimate the initial speed of that car assuming a level road.

Explanation:

As we know that friction force on the car during it applied brakes is given as

so the deceleration of the car is given as

now we can use kinematics to find the initial speed of the car

so we will have

now plug in all the data in it

a skateboard rolling across the street - apex

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.