8. Um automóvel percorre uma estrada com função horária s = – 80 + 80.t, onde s é dado em km e t em horas. O automóvel passa pelo km zero após:stion *
a) 1,0 h.
b) 1,5 h.
c) 0,5 h.
d) 2,0 h.
e) 2,5 h.

a) t = 1.0h

Explanation:

You have the following equation for the position of a car:

To find the value of the time t, in which the car position is zero km you equal s to zero, and then you calculate the time t:

hence, the time in which the position of the car is at s=0 km is t = 1.0h

a) 1.0 h

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.