"Based on the following data, determine if the driver who crashed was driving over the speed limit"
The relevant data given is:
-A 2002 Volvo t-bones a truck in an alley with a speed limit of 20km/h
-An eyewitness heard tires screech, then a loud bang, and also said the driver hit the brakes at the last second, and was going too fast to stop
-Skid marks created by the car were 18.3m in length, with a consistent acceleration of 3.9m/s^2
-A doctor states in a medical record that the bruising and lacerations from the crash are from an impact of 25g's
-The doctor also said that the crash couldn't have been longer than 1/20th of a second
v = d/t
vf = vi + at
d = ( (vf - vi) / 2)*t
d = ( vi*t ) + ( .5*a*t2 )
d = ( vf*t ) - ( .5*a*t2 )
vf2 = vi2 + 2*a*d
The Attempt at a Solution
My thought process so far was to work backwards with a d/t, v/t, and a/t graph. I believe there is four "sections" to the graphs, before the crash, breaking, the crash, and the rolling back from the impact.
I believe the skid marks relate to the breaking motion, while the acceleration given is related to the reverse motion after the crash. I believe the crash portion of the graphs is all zero, except displacement.
I'm stuck for how to continue after this point. The before and after the crash sections will have an unknown time, and seem impossible to solve without the time.