Kinematics?

Question

To stop a car, first you require a certain reaction time to begin braking. Then the car slows down at a constant rate. Suppose that the total distance moved by your car during these two phases is 56.7 m when its initial speed is 75.0 km/h, and 24.4 m when the initial speed is 42.8 km/h. (a) What is your reaction time? s (b) What is the magnitude of the deceleration

How would I figure this out

That didn't work. I know you have to convert km/h to m/s

Answer 1

The distance related to time at constant velocity is
d=v*t

since there is also a decelleration when you take your foot off the gas
d=v*t-.5*a*t^2

find t for the two distances and speeds and average

56.7= 75*t-.5*a*t^2
and
24.4=42.8*t-.5*a*t^2


56.7-24.4=(75-42.8)*t
t=1 second



56.7= 75*1-.5*a*1^2
a = 36.6 m/s^2

check

24.4=42.8*1-.5*a*1^2

a=36.8 close enough


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