An automobile is traveling on a long, straight highway at a steady 71.0 mi/h whe

Question

An automobile is traveling on a long, straight highway at a steady 71.0 mi/h when the driver sees a wreck 200 m ahead. At that instant, she applies the brakes (ignore reaction time). Between her and the wreck are two different surfaces. First there is 140 m of ice, where the deceleration is only 1.30 m/s^2. From then on, it is dry concrete, where the deceleration is a more normal 7.30 m/s^2.

Questions Asked:

1) What was the car’s speed just after leaving the icy portion of the road?
A: 25.4 M/S

2) What is the total distance her car travels before it comes to a stop?
A: 184 M

3) What is the total time it took the car to stop?
A: ????

71 Mi/h = 31.74 M/s

Explanation / Answer

similar problem

71.0 mi/h = 31.73984 m/s

a)
On ice
v^2 = (31.73984)^2 - 2(140) =727.417
answer v = 26.97 m/s

On concrete

(26.97)^2 = 0 - 2(7.30)x
727.38/ 14.6 = x = 49.82 meters

b)
140 +44 = 184 meters

c)

t(ice) = 31.74 - 26.97 = 4.77s

on concrete

26.97 -7.3t = 0
t = 3.69 s

Total time = 4.77 + 3.69 = 8.46 seconds

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