David Sang and Graham Jones Solutions for Chapter: Accelerated Motion, Exercise 7: Questions

Trials on the surface of a new road show that, when a car skids to a halt, its acceleration is $-7.0 \mathrm{m} {\mathrm{s}}^{-2}$. Estimate the skid-to-stop distance of a car travelling at a speed limit of $30 \mathrm{m} {\mathrm{s}}^{-1}$(approximately $110 \mathrm{km} {\mathrm{h}}^{-1}$or $70 \mathrm{mph}$). 

At the scene of an accident on a country road, police find skid marks stretching for $50 \mathrm{m}$. Tests on the road surface show that a skidding car decelerates at $6.5 \mathrm{m} {\mathrm{s}}^{-2}$. Was the car that skidded exceeding the speed limit of $25 \mathrm{m} {\mathrm{s}}^{-1}$$\left(90 \mathrm{km} {\mathrm{h}}^{-1}\right)$ on this road?