Calculating Stopping Distance: Reaction Time and Acceleration in Automobiles

[courtrigrad]

The reaction time of an automobile driver is about 0.7 s. (reaction time is interval between the perception of a signal to stop and the application of the brakes). If an automobile can slow down with an acceleration of -4.0 m/s^2. compute total distance convered in coming to a stop after a signal is observed (a) from an initial speed of 6.7 m/s in a school zone; (b) from an initial speed of 24.6 m/s.

(a) So I know that v_{x} = 0, v_{x}_{0} = 6.7 m/s, a_{x} = -4.0 m/s^{2}. So would I first find time by using 0 = 6.7 - 4t or t = 1.675 s. Then would I add 0.7 seconds to that to get total time? And then use x = x_{0} + v_{x}_{0}t + \frac{1}{2}a_{x}t^{2}. I think something is wrong, but ont know what.

Any help is appreciated

Thanks

 

[Norman]

This seems like the exact solution method. Why do you think it is wrong?