The stopping sight distance for a car traveling at 50 mph is 461 ft (including both perception-reaction distance and braking distance). The perception-reaction time is 2.5 sec. If a car traveling at 60 mph is to stop in the same distance with the same deceleration, what is most nearly the required perception-reaction time

2.08 s

Explanation:

We are given that

Speed,v=50mph=73.3ft/s

1 mile=5280 feet

1 hour=3600 s

Distance,d=461 ft

t=2.5 s

v'=60 mph=88 ft/s

We have to find the perception reaction time.

Perception reaction distance=

f is prop to m1xm2 double m1 double force

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.