Chapter 5.7, Problem 33ES

In these exercises assume that the object is moving with constant acceleration in the positive direction of a coordinate line, and apply Formulas $\left(10\right)$ and $\left(11\right)$ as appropriate. In some of these problems you will need the fact that $88\text{ ft/s}=60\text{ mi/h}$ .

Spotting a police car, you hit the brakes on your new Porsche to reduce your speed from $90\text{ mi/h}$ to $60\text{ mi/h}$ at a constant rate over a distance of $200\text{ ft}$ .

(a) Find the acceleration in ${\text{ft/s}}^{\text{2}}$ .

(b) How long does it take for you to reduce your speed to $55\text{ mi/h}$ ?

(c) At the acceleration obtained in part (a), how long would it take for you to bring your Porsche to a complete stop from $90\text{ mi/h}$ ?