stopping distance?

Question

Determine the stopping distances for an automobile with an initial speed of 95 km/h and human reaction time of 3.0 s for the following accelerations.
(a) a = -4.0 m/s2
(b) a = -8.0 m/s2

Answer 1

First, the car will travel at constant speed for 3.0 seconds
Then it will stop according to v(t)=v0-a*t
solve for t and then plug into
x(t)=v0*t-.5*a*t^2

add the two together for your answer

j

Answer 2

First convert 95 Km/h to meters/sec

95*1000/3600 = 26.3889 m/s

Then calculate the distance for the reaction time

D= vt = 26.3889*3 = 79.2 meters

Then calculate the stopping distance

For a = -4 m/s^2 : D=V^2/(2a) = 26.3889^2/(2(4)) = 87.05 m
For a = -8 m/s^2 : D= V^2/(2a) = 26.3889^2/(2(8)) = 43.52 m

Now add the stopping distance to the reaction distance:

79.2 + 87.05 = 166.25 m
and
79.2 + 43.52 = 122.72 m

So your answers are 166.25 meters and 122.72 meters.